Carbonate Petrography

Carbonate petrography is the study of limestones, dolomites and associated deposits under optical or electron microscopes greatly enhances field studies or core observations and can provide a frame of reference for geochemical studies.

25 strangest Geologic Formations on Earth

The strangest formations on Earth.

What causes Earthquake?

Of these various reasons, faulting related to plate movements is by far the most significant. In other words, most earthquakes are due to slip on faults.

The Geologic Column

As stated earlier, no one locality on Earth provides a complete record of our planet’s history, because stratigraphic columns can contain unconformities. But by correlating rocks from locality to locality at millions of places around the world, geologists have pieced together a composite stratigraphic column, called the geologic column, that represents the entirety of Earth history.

Folds and Foliations

Geometry of Folds Imagine a carpet lying flat on the floor. Push on one end of the carpet, and it will wrinkle or contort into a series of wavelike curves. Stresses developed during mountain building can similarly warp or bend bedding and foliation (or other planar features) in rock. The result a curve in the shape of a rock layer is called a fold.

Tuesday, 27 December 2016

10 of the Best Learning Geology Photos of 2016

A picture is worth a thousand words, but not all pictures are created equal. The pictures we usually feature on Learning Geology are field pictures showing Geological structures and features and many of them are high quality gem and mineral pictures. The purpose is to encourage students and professionals' activities by promoting "learning and scope" of Geology through our blogs.
In the end of 2016, we are sharing with you the 10 best photos of 2016 which we have posted on our page.

P.S: we always try our best to credit each and every photographer or website, but sometimes it’s impossible to track some of them. Please leave a comment if you know about the missing ones.

1. Folds from Basque France

 Image Credits: Yaqub ShahYaqub Shah

2. Horst and Graben Structure in Zanjan, Iran


Image Credits: https://www.instagram.com/amazhda



3. A unique Normal Fault

4. The Rock Cycle
The
 rock cycle illustrates the formation, alteration, destruction, and reformation of earth materials, and typically over long periods of geologic time. The rock cycle portrays the collective system of processes, and the resulting products that form, at or below the earth surface.The illustration below illustrates the rock cycle with the common names of rocks, minerals, and sediments associated with each group of earth materials: sediments, sedimentary rocks, metamorphic rocks, and igneous rocks.


Image Credits: Phil Stoffer


5. An amazing Botryoidal specimen for Goethite lovers! 


Image Credits: Moha Mezane 
   

6. Basalt outcrop of the Semail Ophiolite, Wadi Jizzi, Oman

Image Credits: Christopher Spencer
Christopher Spencer is founder of an amazing science outreach program named as Traveling Geologist. Visit his website to learn from him


7. Val Gardena Dolomites, Northern Italy





8. Beautiful fern fossil found in Potsville Formation from Pennsylvania.
The ferns most commonly found are Alethopteris, Neuropteris, Pecopteris, and Sphenophyllum.


Image Credits: Kurt Jaccoud


9. Snowball garnet in schist

Syn-kinematic crystals in which “Snowball garnet” with highly rotated spiral Si. 

Porphyroblast is ~ 5 mm in diameter.
From Yardley et al. (1990) Atlas of Metamorphic Rocks and their Textures.



10. Trilobite Specimen from Wheeler Formation, Utah
The Wheeler Shale is of Cambrian age and is a world famous locality for prolific trilobite remains. 


Image Credits: Paleo Fossils

Saturday, 24 December 2016

Morganite

What is Morganite?

Morganite is the pink to purplish-pink variety of Beryl. Beryl is best known for its gem varieties Emerald and Aquamarine, but other gem forms such as Morganite are also used. Morganite was first identified in 1910, and was named the following year by George F. Kunz in honour of financier and banker J.P. (John Pierpont) Morgan. Morgan was an avid collector of gemstones.

History and Introduction

Morganite is the light pink to violet-pink variety of beryl. Since beryl is most famous for being the mineral group that green emerald belongs to, pink morganite is sometimes referred to as 'pink emerald'. Along with emerald, morganite is also related to blue aquamarine, golden beryl (heliodor), colourless goshenite and the rare red bixbite. Among the beryls, morganite is one of the rarest forms, second only to red bixbite.
Pink morganite was first identified in Madagascar, in 1910 and known as 'pink beryl'. Shortly thereafter, George D. Kunz, a famous American gemologist and buyer for Tiffany & Company renamed it in honor of John Pierpont (J.P.) Morgan, an American banker and avid gemstone collector. Since its discovery, morganite has been prized by gem collectors owing to its rarity.

Identifying Morganite

Morganite is an aluminium beryllium silicate. Its colour can range from pale pink to violet, salmon or peach. Along with other beryls, morganite has very good hardness, with a rating of 7.5 to 8 on the Mohs scale. The refractive index is 1.562 to 1.602. Beryl generally has a specific gravity of 2.66 to 2.87, but morganite is slightly denser than other beryls at 2.71 to 2.90. Morganite is usually quite clean, unlike emerald which tends to be heavily included. In most cases, morganite can be easily distinguished from other pink stones by its brilliance and luster, combined with its hardness, durability and excellent clarity.

Morganite: Origin and Sources

Morganite can be found in many locations around the world. The two most significant deposits are found in Brazil and Madagascar. Other notable sources for fine gem-quality morganite include Afghanistan, China, Madagascar, Mozambique, Namibia, Russia, Zimbabwe and the USA (California and Maine).

Morganite: Related or Similar Gemstones

Morganite belongs to the very important beryl group of gemstones and minerals. There are several closely related gemstone varieties of beryl, typically classified by colour or impurities. Some of the more popular beryls related to pink morganite include green emerald, blue aquamarine, white goshenite and golden beryl or heliodor.
The rarest beryl is red bixbite. Bazzite and pezzottaite are often considered to be types of beryl because they are very similar, but gemologically, they are not technically true beryls. Morganite may sometimes be referred to as 'pink emerald' or as 'rose beryl', but these are simply marketing names.

Famous Morganite Gemstones

The world's largest faceted morganite is a cushion-shaped morganite from Madagascar that weighs nearly 600 carats. It is currently exhibited in the British Museum collection.

Determining Morganite Value

Morganite Colour

Morganite ranges in colour from pale pink to pink, violet-pink, peach, peachy-pink, or salmon colour. Its colour is thought to be owed to traces of manganese or cesium. Morganite is rarely vivid or intense in colour; most stones are very pale or pastel coloured. Large stones will typically exhibit stronger colours. A pure pink morganite is considered most desirable but more recently, peachy and salmon coloured stones have been in very high demand. There is also a rare magenta coloured morganite from Madagascar that is highly sought after by collectors.

Morganite Clarity and Luster

Morganite occurs with excellent transparency. Unlike emerald, it rarely forms with inclusions, thus, eye-clean stones are expected. Morganite exhibits an attractive vitreous luster when cut and polished.

Morganite Cut and Shape

Morganite is typically faceted to maximize its colour and brilliance. With its indistinct cleavage, cutters must orient the stone properly to minimise cleavage. Rare materials which exhibit chatoyancy (cat's eye effect) are often cut en cabochon in order to best exhibit desirable effects. Morganite is most often cut into rounds ovals, cushions and pears, as well as trillions, hearts and briolettes.

Morganite Treatment

Morganite is often found unheated and unenhanced. However, many stones today may be routinely heat treated to improve colour and remove unwanted yellow tones. Heating is done at relatively low temperatures (about 400 degrees centigrade) to achieve this effect.

Properties of Morganite

Chemical FormulaBe3Al2SiO6
ColourPink, Purple
Hardness7.5 - 8
Crystal SystemHexagonal
Refractive Index1.57 - 1.58
SG2.6 - 2.8
TransparencyTransparent to translucent
Double Refraction.006
LusterVitreous
Cleavage3,1 - basal
Mineral ClassBeryl

Moonstone

What is Moonstone?

Moonstone is the most well-known gemstone of the feldspar group. Named for its glowing colour sheen that resembles the moonlight, Moonstone can belong to several different members of the feldspar group, especially Orthoclase and Oligoclase. Moonstone displays a unique play of colour known as adularescence. This effect is in the form of a moving floating light or sheen. This phenomenon is caused by structural anomalies within the crystal formation.

History and Introduction

Moonstone is the most well-known gemstone variety of orthoclase feldspar, a potassium aluminium silicate. It is a transparent to opaque oligoclase, a variety of plagioclase albite and sheet mica. Moonstone is known to exhibit a distinct sheen under certain lighting conditions, and it is the sheen which renders moonstone one of the most remarkable gemstones available today. In fact, its name is owed to the almost magical, bluish white shimmer it exhibits, which closely resembles that of the moon. Gemologists refer to the shimmering optical phenomena as 'adularescence'.
The optical effect of adularescence is a result of moonstone's unique structural pattern. Tiny inclusions of albite, a sodium aluminium silicate are intermixed with host rock layers of orthoclase, a potassium aluminium silicate. The alternating layers of different feldspars form a lamellar (scaly) structure which causes the interference of light as it enters the stone. Thin layers of alternating silicates tend to refract more attractive and colourful sheens, whereas thick layers of silicates produce less attractive, white to colourless sheens. As light enters the stone, it is refracted and scattered, producing an extremely unique and attractive play of both colour and light. With moonstone, the aura of light actually appears to glow from deep within the surface of the stone.

World-famous Moonstone

Moonstone was extremely popular in the times of "Art Nouveau", which took place more than 100 years ago. It was used to decorate a striking amount of pieces of gemstone jewellery created by the famous French Master-Goldsmith, René Lalique, as well as many of his contemporaries. His rare pieces are typically only found in museums or in well-guarded private collections.

Identifying Moonstone

Moonstone can be identified by the presence of adularescence. Other gems with a similar appearance do not have the phenomenal presence of adularescence which makes identification of moonstone fairly easy. Moonstone is a potassium aluminium silicate and can be easily identified by composition. Many similar materials, such as labradorite, are actually plagioclase feldspar, whereas moonstone is by composition a potassium feldspar. Testing for hardness is often one of the easiest methods for distinguishing moonstone from other materials. Other similar gems, such as opal, chalcedony or ammolite, are significantly harder or softer than moonstone. Top quality moonstone can show an incredible "three-dimensional" depth of colour, which no other gemstone can replicate, making moonstone almost unmistakable.

Moonstone Origin and Gemstone Sources

Moonstone deposits are often found as constituents in feldspar-rich granitic and syenitic pegmatites all over the world. The most important moonstone deposits are from Sri Lanka and India. Other notable sources include Australia, Brazil, Germany, India, Myanmar (Burma), Madagascar, Mexico, Norway, Switzerland, Tanzania, and the United States. Sri Lankan moonstone is most famous for its attractive blue coloured material, but blue moonstone is becoming increasingly rare. India is known for producing fine 'rainbow moonstone'. Switzerland's Adula Mountains possess the most historically interesting moonstone mines.

Moonstone: Varieties or Similar Gemstones

Moonstone belongs to the large group of feldspar minerals, the most abundant minerals on earth. The feldspars make up approximately 60% of the Earth's crust, which means there are many moonstone-related gems and minerals. Quartz gemstones make up the second most abundant gemstone group, second only to the feldspar family.
Feldspars are typically classified into two main gemstone groups: Potassium feldspar and plagioclase feldspar. All varieties of moonstone are potassium feldspar. Other potassium feldspar gemstones include amazonite and orthoclase. There are also several gemstones which are often confused with moonstone based on appearance alone, such as 'rainbow moonstone'. Rainbow moonstone is actually not a true moonstone, but rather, it is a variety of labradorite plagioclase feldspar. This is why it is sometimes referred to as 'blue-sheen labradorite'.
Most Popular Similar or Related Trade Names & Gemstones:
Star moonstone, cat's eye moonstone, rainbow moonstone and sunstone are the most popular and well-known trade names used for similar or related gemstones.
Lesser-Known Similar or Related Trade Names & Gemstones:
Orthoclase, amazonite, labradorite, andesine, andesine-labradorite and oligoclase are the lesser-known trade names used for similar or related gemstones.

Properties of Moonstone

Chemical FormulaPlagioclase Feldspar: (Na,Ca)Al1-2Si3-2O8
Orthoclase Feldspar: KAlSi3O8
ColourWhite, Colorless, Blue, Green, Yellow, Orange, Brown, Pink, Purple, Gray
Hardness6 - 6.5


Refractive Index1.518 - 1.526
SG2.56 - 2.62
TransparencyTransparent to translucent
Double Refraction-.0005
LusterPearly
Cleavage2,1 - basal ; 2,1 - prismatic ; 3,1 - pinacoidal
Mineral ClassOrthoclase, Oligoclase, and other members of the feldspar group

Malachite

What is Malachite?

Malachite is a green copper carbonate hydroxide mineral with a chemical composition of Cu2(CO3)(OH)2. It was one of the first ores used to produce copper metal. It is of minor importance today as an ore of copper because it is usually found in small quantities and can be sold for higher prices for other types of use.
Malachite has been used as a gemstone and sculptural material for thousands of years and is still popular today. Today it is most often cut into cabochons or beads for jewellery use.
Malachite has a green colour that does not fade over time or when exposed to light. Those properties, along with its ability to be easily ground to a powder, made malachite a preferred pigment and colouring agent for thousands of years.

Where Does Malachite Form?

Malachite is a mineral that forms at shallow depths within the Earth, in the oxidising zone above copper deposits. It precipitates from descending solutions in fractures, caverns, cavities, and the inter-granular spaces of porous rock. It often forms within limestone where a subsurface chemical environment favourable for the formation of carbonate minerals can occur. Associated minerals include azurite, bornite, calcite, chalcopyrite, copper, cuprite, and a variety of iron oxides.
Some of the first malachite deposits to be exploited were located in Egypt and Israel. Over 4000 years ago, they were mined and used to produce copper. Material from these deposits was also used to produce gemstones, sculptures, and pigments. Several large deposits in the Ural Mountains of Russia were aggressively mined, and they supplied abundant gem and sculptural material in the 1800s. Very little is produced from these deposits today. Much of the malachite entering the lapidary market today is from deposits in the Democratic Republic of the Congo. Smaller amounts are produced in Australia, France, and Arizona.

Physical Properties of Malachite

Malachite's most striking physical property is its green colour. All specimens of the mineral are green and range from a pastel green, to a bright green, to an extremely dark green that is almost black. It is typically found as stalactites and botryoidal coatings on the surfaces of underground cavities similar to the deposits of calcite found in caves. When these materials are cut into slabs and pieces, the sawn surfaces often exhibit banding and eyes that are similar to agate.
Malachite is rarely found as a crystal, but when found, the crystals are usually acicular to tabular in shape. The crystals are bright green in colour, translucent, with a vitreous to adamantine luster. Non-crystalline specimens are opaque, usually with a dull to earthy luster.
Malachite is a copper mineral, and that gives malachite a high specific gravity that ranges from 3.6 to 4.0. This property is so striking for a green mineral that malachite is easy to identify. Malachite is one of a small number of green minerals that produces effervescence in contact with cold, dilute hydrochloric acid. It is also a soft mineral with a Mohs hardness of 3.5 to 4.0.

Malachite as a Pigment

Malachite has been used as a pigment for thousands of years. It was one of the oldest known green pigments to be used in paintings. The mineral malachite is an excellent material for producing a powdered pigment because it can easily be ground into a fine powder, it mixes easily with vehicles, and it retains its colour well when exposed to light over time.
Alternative names for malachite pigment include copper green, Bremen green, Olympian green, green verditer, green bice, Hungarian green, mountain green, and iris green. Malachite pigment is found in the paintings of Egyptian tombs and in paintings produced throughout Europe during the 15th and 16th centuries. Its use declined significantly in the 17th century as alternative green colours were developed. Today, malachite pigment is sold by a few manufacturers who specialise in providing materials to painters who practice historically accurate techniques.

Malachite as a Gem Material

The vivid green colour, bright polished luster, banding and eyes of malachite make it very popular as a gemstone. It is cut into cabochons, used to produce beads, sliced into inlay material, sculpted into ornamental objects, and used to manufacture tumbled stones. Small boxes made from slices of malachite are attractive and popular.
Some of the most spectacular gem-quality malachite involves intergrowths, inclusions, and admixtures of malachite with other copper minerals such as azurite (azurmalachite), chrysocolla, turquoise, and pseudomalachite (eilat stone).
Malachite's use as gem and ornamental stone is limited by its properties. It has perfect cleavage and a Mohs hardness of 3.5 to 4. These limit its use to items that will not suffer abrasion and impact. It is also sensitive to heat and reacts with weak acids. These properties further limit its use and require care during cleaning, repair, and maintenance. Malachite is sometimes treated with wax to fill small voids and improve its luster.
Synthetic malachite has been produced and used to make jewellery and small sculptures. Poorly done synthetics are often recognised by their unnatural colour. The better synthetics can usually be recognised because their banding and eyes do not have a natural geometry. An experienced person can identify most of the synthetic and imitation materials on sight.

Properties of Malachite

Chemical FormulaCu2CO3(OH)2
ColourGreen, Banded
Hardness3.5 - 4
Crystal SystemMonoclinic
Refractive Index1.65 - 1.91
SG3.9 - 4.0
TransparencyOpaque
Double Refraction-.025
LusterSilky
Cleavage1,1 - basal. Not usually discernible because crystals are tiny.
Mineral ClassMalachite

Larimar Gemstone

What is Larimar?

Larimar is a blue variety of the mineral Pectolite. Pectolite is not a rare mineral and is found throughout the world, but the exquisite sea-blue colour exhibited in the Larimar variety is very unique, and only comes from one place in the world. It is found only in a limited deposit in the Dominican Republic, and is virtually the only gemstone to be found in the entire Caribbean. Its lovely sea-blue colour is very reminiscent of the Caribbean seas.

History

The Dominican Republic's Ministry of Mining records show that on 23 November 1916, Father Miguel Domingo Fuertes Loren of the Barahona Parish requested permission to explore and exploit the mine of a certain blue rock he had discovered. Pectolites were not yet known in the Dominican Republic, and the request was rejected.
In 1974, at the foot of the Bahoruco Range, the coastal province of Barahona, Miguel Méndez and Peace Corps volunteer Norman Rilling rediscovered Larimar on a beach. Natives, who believed the stone came from the sea, called the gem Blue Stone. Miguel took his young daughter's name Larissa and the Spanish word for sea (mar) and formed Larimar, by the colours of the water of the Caribbean Sea, where it was found. The few stones they found were alluvial sediment, washed into the sea by the Bahoruco River. An upstream search revealed the in situ outcrops in the range and soon the Los Chupaderos mine was formed.

Occurrence

Larimar is a type of pectolite, or a rock composed largely of pectolite, an acid silicate hydrate of calcium and sodium. Although pectolite is found in many locations, none have the unique volcanic blue coloration of larimar. This blue colour, distinct from that of other pectolites, is the result of copper substitution for calcium.
Miocene volcanic rocks, andesites and basalts, erupted within the limestones of the south coast of the island. These rocks contained cavities or vugs which were later filled with a variety of minerals including the blue pectolite. These pectolite cavity fillings are a secondary occurrence within the volcanic flows, dikes and plugs. When these rocks erode the pectolite fillings are carried downslope to end up in the alluvium and the beach gravels. The Bahoruco River carried the pectolite bearing sediments to the sea. The tumbling action along the streambed provided the natural polishing to the blue larimar which makes them stand out in contrast to the dark gravels of the streambed.

Los Chupaderos

The most important outcrop of blue pectolite is located at Los Chupaderos, in the section of Los Checheses, about 10 km (6.2 mi) southwest of the city of Barahona, in the south-western region of the Dominican Republic. It is a single mountainside now perforated with approximately 2,000 vertical shafts, surrounded by rainforest vegetation and deposits of blue-coloured mine tailing.

Jewellery

Larimar jewellery is offered to the public in the Dominican Republic, and elsewhere in the Caribbean as a local speciality. Most jewellery produced is set in silver, but sometimes high-grade larimar is also set in gold. It also has become available elsewhere. Some Far East manufacturers have started to use it in their production and buy large quantities of raw stones as long as this is still permitted.
Quality grading is according to coloration and the typical mineral crystal configuration in the stone. Larimar also comes in green and even with red spots, brown strikes, etc., due to the presence of other minerals and/or oxidation. But the more intense the blue colour and the contrast in the stone, the higher and rarer is the quality. The blue colour is photosensitive and fades with time if exposed to too much light and heat.

Properties of Larimar

Chemical FormulaNaCa2Si3O8(OH)
ColourBlue, Green, Multicolored
Hardness4.5 - 5
Crystal SystemTriclinic
Refractive Index1.59 - 1.65
SG2.7 - 2.9
TransparencyTranslucent to opaque
Double Refraction0.038
LusterSilky
Cleavage2,2
Mineral ClassPectolite

Lapis Lazuli

What is Lapis Lazuli?

Lapis lazuli, also known simply as "lapis", is a blue metamorphic rock that has been used by people as a gemstone, sculpting material, and ornamental material for thousands of years.
Unlike most other gem materials, lapis lazuli is not a mineral. Instead, it is a rock composed of multiple minerals. The blue colour of lapis lazuli is mainly derived from the presence of lazurite, a blue silicate mineral of the sodalite group with a chemical composition of (Na,Ca)8(AlSiO4)6(S,Cl,SO4,OH)2.

Geologic Occurrence of Lapis Lazuli

Lapis lazuli forms near igneous intrusions where limestone or marble has been altered by contact metamorphism or hydrothermal metamorphism. In these rocks, lazurite replaces portions of the host rock and often preferentially develops within certain bands or layers.
Afghanistan is the world's leading source of lapis lazuli. Some parts of the country have been actively mined for thousands of years. Other countries that produce notable amounts of lapis lazuli include Chile, Russia, Canada, Argentina, and Pakistan. In the United States small amounts of lapis lazuli have been produced in California, Colorado, and Arizona.

Composition and Properties of Lapis

In addition to lazurite, specimens of lapis lazuli usually contain calcite and pyrite. Sodalite, hauyne, wollastonite, afghanite, mica, dolomite, diopside, and a diversity of other minerals might also be present. To be called "lapis lazuli," a rock must have a distinctly blue colour and contain at least 25% blue lazurite.
Calcite is often the second most abundant mineral present in lapis lazuli. Its presence can be very obvious, appearing as white layers, fractures, or mottling. It can also be finely intermixed with lazurite to produce a rock with a faded denim colour.
Pyrite usually occurs in lapis lazuli as tiny, randomly spaced grains with a contrasting gold colour. When abundant, the grains can be concentrated or inter-grown into distinct layers or patches. It can occasionally occur as a fracture-filling mineral.
As a rock, lapis lazuli is composed of several minerals, each with its own hardness, cleavage/fracture characteristics, specific gravity, and colour. Hardness ranges from a Mohs 3 for calcite to the 6.5 of pyrite. The hardness of the material depends upon where you test it.

History of Lapis Lazuli

Lapis lazuli has been popular through most of recorded human history. Mining for lapis occurred in the Badakhshan Province of northeastern Afghanistan as early as 7000 BC. The lapis was used to make beads, small jewellery items and small sculptures. These have been found at Neolithic archaeological sites dating back to about 3000 BC in Iraq, Pakistan, and Afghanistan.
Lapis lazuli appears in many Egyptian archaeological sites that date back to about 3000 BC. It was used in many ornamental objects and jewellery. Powdered lapis was used as a cosmetic and a pigment.
In Biblical times the word "sapphire" was often used as a name for lapis lazuli. For that reason, many scholars believe that at least some of the references to sapphire in the Bible are actually references to lapis lazuli. Some modern translations of the Bible use the word "lapis" instead of "sapphire."
Lapis lazuli started to be seen in Europe during the Middle Ages. It arrived in the form of jewellery, cutting rough, and finely ground pigment.
Today lapis lazuli is still used in jewellery and ornamental objects. As a pigment it has been replaced with modern materials except by artists who strive to use historical methods.

Lapis Lazuli as a "Conflict Mineral"?

Afghanistan has been one of the world's primary sources of lapis lazuli through most of recorded history. Most of the country's production comes from thousands of small mines in the Badakhshan Province. This is an area with a destitute economy, where opium poppy growing and gemstone mining are the only important sources of outside revenue.
Much of the area where the lapis lazuli mining occurs is occupied by the Taliban and local members of the Islamic State. They operate illegal mines, attack other mines to capture their production, and demand protection payments from intimidated mine operators. Revenue from these activities is used to fund war and terrorism.
Numerous advocacy groups and some members of the Afghanistan government would like to see Afghanistan's lapis lazuli classified as an international "conflict mineral." This would require the country's government to track the production and sale of lapis lazuli from mine to market. It would also involve an international effort to keep illicit lapis lazuli from being traded. The Kimberly Process, used for tracking the flow of diamonds, would serve as a model for the tracking of illicit lapis lazuli.

Use as a Gem and Ornamental Material

Lapis lazuli is most widely known for its use as a gemstone. It is a popular material for cutting into cabochons and beads. It is also used in inlay or mosaic projects and often as a material for small sculptures. These uses made lapis the most popular opaque blue gemstone.
Although personal preferences vary, the most popular lapis has a uniform, deep blue to violet blue colour. Many people enjoy a few randomly placed grains of gold pyrite or a few fractures or mottles of white calcite. However, when pyrite or calcite is present in more than minor amounts, the desirability of the material and the value are significantly lowered. Gray inclusions or mottling also quickly lowers desirability.
Lapis lazuli has some durability problems that limit its suitability for certain uses. Lapis has a Mohs hardness of about 5, which makes it very soft for use in a ring, cuff links or bracelet - especially if the top of the stone is raised above the top of the setting or bezel. In these uses, lapis will show signs of abrasion with continued use.
Lapis is best used in earrings, pins, and pendants, where abrasion is less likely to occur. When stored as unmounted stones or in jewellery, lapis can be damaged if the pieces are not isolated from one another. Jewellery is best stored in separate boxes or bags, or in trays with separate compartments for each item. Loose cut stones should be stored in separate papers, in bags, or in gem containers where the stones will not rub or abrade one another.

Treatment of Lapis Lazuli

Lapis lazuli is frequently treated after it is cut and before it is sold as finished gemstones, sculptures, or ornaments. Lapis lazuli is slightly porous and that allows it to accept and hold dye. Much of the material that enters the market has been treated with a blue dye to remove the visibility of white calcite. It is then frequently treated with wax or oil that improve the luster of polished surfaces and seal the dyed calcite.

Lapis Lazuli Used as a Pigment

High-quality lapis lazuli has been used as a mineral pigment for over 1,000 years. Bright blue pieces of lapis are trimmed of impurities and ground to a fine powder; the powder can then be mixed with oil or another vehicle for use as a paint.
Higher-grade pigments can be produced by washing the powder with mild acid to remove calcite and dolomite that dilute the blue colour. The material is then processed to remove grains of pyrite and other foreign minerals. This lapis-derived pigment was named "ultramarine blue," a name that has been subsequently used for hundreds of years.
During the Renaissance and into the 1800s, paintings done with ultramarine blue were considered to be a luxury because of their high cost. High-quality lapis lazuli was mined in Afghanistan and transported to Europe to manufacture ultramarine blue. This costly pigment was normally used by only the most accomplished artists and those who had wealthy clients to support the additional expense.
Ultramarine blue made from lapis lazuli is one of the few natural pigments with a permanent and vivid blue colour, good opacity, and high stability. It has always been very expensive and today can sell for over $1,000 per pound.
Starting in the mid-1800s, artists and chemists began developing synthetic blue pigments for use as alternatives to ultramarine blue made from lapis lazuli. Some of these pigments also bear the name "ultramarine." An artist who wants an ultramarine pigment made from lapis lazuli today must be sure that the pigment is not synthetic and is actually made from lapis lazuli. Synthetic ultramarine pigments have their advantages. Their blue colour is usually deeper and more consistent than traditional ultramarine, and they also cost far less.
Today, because of cost, very little ultramarine made from lapis lazuli is used, mainly by artists who are striving to learn historical techniques or achieve results similar to master painters of the past. It is prepared by a few pigment manufacturers who continue to use lapis lazuli from the historical sources in Afghanistan.

Examples of Ultramarine in Paintings

A few master painters (examples of which are provided below) considered the use of ultramarine and other costly pigments an essential part of producing paintings with optimum colour.
Vincent Van Gogh (1853-1890) used ultramarine to paint The Starry Night in 1889. The oil on canvas painting is considered to be one of his best works and is today in the collection of the Museum of Modern Art in New York City. It is a widely recognised painting.
Johannes Vermeer (1632-1675) used ultramarine to paint the headscarf of the Girl with a Pearl Earring in about 1665. The oil on canvas painting has been exhibited at museums throughout the world, and also served as the inspiration for a novel and a film. It is currently in the collection of the Mauritshuis in The Hague.
Titian (1488-1576) used ultramarine blue to paint the dramatic sky and draperies in his oil on canvas painting of Bacchus and Ariadne. The painting is now on display at the National Gallery in London.
Many painters have used ultramarine blue to paint the robe of Mary, mother of Jesus. Giovanni Sassoferrato (1609-1685) produced one of the most vivid examples when he painted The Virgin in Prayer between 1640 and 1650. The oil on canvas painting is on exhibit at the National Gallery in London.

Properties of Lapis Lazuli

Chemical FormulaThe chief constituent Lapis Lazuli is Lazurite, with the following chemical formula:
(Na,Ca)8Al6Si6O24(S,SO)4
ColourBlue, Multicoloured
Hardness5 - 5.5
Crystal SystemIsometric
Refractive Index1.5
SG2.4 - 2.5
TransparencyOpaque
Double RefractionNone
LusterVitreous to greasy
Cleavage3,6
Mineral ClassRock that is mostly Lazurite with minor Calcite, Pyrite, and other minerals