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.

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

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

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

Kyanite

What is Kyanite?

Kyanite is a mineral found mainly in metamorphic rocks. It most often forms from the high-pressure alteration of clay minerals during the metamorphism of sedimentary rocks. It is found in the schists and gneisses of regionally metamorphosed areas and less often in quartzite or eclogite.
Kyanite's typical habit is a bladed crystal, although it sometimes occurs as radiating masses of crystals. Kyanite is often associated with other metamorphic minerals such as garnet, staurolite, and corundum.

Kyanite's Unusual Hardness

Kyanite specimens have a variable hardness. The long crystals have a Mohs hardness of about 4.5 to 5 if tested parallel to the length of a crystal, and a hardness of 6.5 to 7 if tested across the short dimension of a crystal. The mineral was once commonly called "disthene" which means "two strengths."

Polymorphs of Al2SiO5

Three minerals have a chemical composition of Al2SiO5. These are kyanite, andalusite, and sillimanite. Kyanite is the high-pressure polymorph, sillimanite forms at high temperature, and andalusite is the low-pressure polymorph.

Many Industrial Uses of Kyanite

Kyanite is used to manufacture a wide range of products. An important use is in the manufacture of refractory products such as the bricks, mortars, and kiln furniture used in high-temperature furnaces. For foundries, the molds that are used for casting high-temperature metals are often made with kyanite.
Kyanite is also in products used in the automotive and railroad industries where heat resistance is important. Mullite, a form of calcined kyanite, is used to make brake shoes and clutch facings.

Use in High-Refractory-Strength Porcelain

Kyanite has properties that make it exceptionally well suited for the manufacture of a high-refractory-strength porcelain - a porcelain that holds its strength at very high temperatures. A familiar use of this type of porcelain is the white porcelain insulator on a spark plug.
Kyanite is also used in some of the more common forms of porcelain, such as those used to make dentures, sinks, and bathroom fixtures.

Use in Abrasive Products

Kyanite's heat resistance and hardness make it an excellent material for use in the manufacture of grinding wheels and cutting wheels. It is not used as the primary abrasive; instead, it is used as part of the binding agent that holds the abrasive particles together in the shape of a wheel.

Expansion of Kyanite When Heated

Kyanite, unlike most other minerals, can expand significantly when heated. Depending upon particle size, temperatures, and heating conditions, kyanite can expand to up to twice its original volume when heated. This expansion is predictable. In the manufacture of certain refractory products, specific amounts of kyanite are added to the raw material (which shrinks during heating) to maintain volume in the finished product.

Kyanite Use as a Gemstone

Kyanite is a gemstone that you will rarely encounter in the typical jewellery store. Most people have not heard of kyanite, as it is infrequently used in jewellery. It is an "exotic" gem. Perhaps that is what makes it so interesting?
If you are interested in kyanite as a gemstone or in jewellery, the best place to find it is in artisan jewellery stores or in jewellery stores that are associated with a mineral dealer. The people who own these businesses are likely to be interested in kyanite and incorporate it into their product line.
High-quality and nicely coloured kyanite can be cut into attractive and desirable cabochons and faceted stones. These are often used in rings, earrings, pendants, and other jewellery. Kyanite is also used to make beads. These beads often have a flat geometry because the mineral typically occurs in thin blades.

Kyanite Gemstones are Challenging to Cut

Kyanite is a challenging mineral to cut because it has two distinctly different hardnesses. Kyanite crystals are typically long, narrow blades. They have a hardness of about 4.5 parallel to their length but a hardness of 6.5 to 7.0 across the width of the blade. Skilled cutters are needed to work these stones.

Blue Kyanite - Green Kyanite

Most gemstone-quality kyanite is blue in colour. However, kyanite can be clear, green, black, and rarely purple. Some kyanite gemstones are pleochroic (appear to be different colours when viewed from different directions).
Blue kyanite stones can be found in a continuous colour range between clear and dark blue. The most popular kyanite gemstones are transparent with a deep sapphire-blue colour. Some deep blue stones are shown in the photos on this page. Transparent blue kyanite with a lower colour intensity might look like blue topaz or blue aquamarine.

Properties of Kyanite

Chemical FormulaAl2SiO5
ColourBlue
Hardness4.5 - 7
Crystal SystemTriclinic
Refractive Index1.71 - 1.73
SG3.5 - 3.7
TransparencyTransparent to translucent
Double Refraction-0.015
LusterVitreous
Cleavage1,1;2,1
Mineral ClassKyanite

Kunzite Gemstone

What is Kunzite?

Kunzite is the pink to light purple gem variety of the mineral Spodumene. Spodumene is a common mineral, but only in several localities does it occur in transparent gem form. The main gem form of Spodumene is Kunzite, the other is the rarer Hiddenite. Yellow and colourless gem forms of Spodumene also exist, but are not commonly faceted as gemstones. Kunzite has a lovely pink colour and is becoming increasingly popular in the gemstone market.
Kunzite forms naturally as colourless, pink, lilac, yellow and green crystals. The yellow-green to emerald variety is known as Hiddenite, or Green Kunzite. The colourless to light yellow variety is known as Triphane, or Spodumene. Genuine Kunzite is quite pale in colour, with natural darker shades being higher in value. There are some heat-enhanced varieties on the market. All Kunzite is prone to fading in direct sunlight.

History and Introduction

Kunzite is the pale pink to light-violet gem-quality variety of the pyroxene mineral spodumene, a lithium aluminum inosilicate. Kunzite was first discovered in Connecticut, USA, and was named after George Frederick Kunz (1856 - 1932), an American mineralogist and the former vice president and buyer for Tiffany & Company. Kunz was a legendary New York jeweller and coloured stone specialist, and he was the first to comprehensively describe the stone in 1902.
Although it was first discovered in the USA, most of the current supply of kunzite is found in Afghanistan and Pakistan. Kunzite is closely related to hiddenite, the yellow-green member of the spodumene gemstone family which was also discovered and named after an American mineralogist, W. E. Hidden; as well as the classic golden to yellow colour gem-quality spodumene. Kunzite is known to produce gemstones of great size. In fact, it's not uncommon to find fine quality stones weighing 20 carats or more. Kunzite and the entire spodumene group are important industrial sources of lithium, which is used for the making of medicines, ceramics, mobile phones and automotive batteries.

World-famous Kunzite

A beautiful 47-carat kunzite ring sold for over $410,000 at a Sotheby's auction of the Estate of Jacqueline Kennedy Onassis in 1996. President Kennedy purchased it as a gift for his wife, but never had the chance to give it to her.

Identifying Kunzite

Courtesy: The Arkenstone
Kunzite is composed of lithium, aluminum and silicate. Kunzite crystallizes in the monoclinic crystal system. Its prismatic crystal structure results in a distinct pleochroism which can be helpful in identifying kunzite. Kunzite exhibits perfect cleavage, a trait it shares with both diamond and topaz. With prolonged exposure to direct sunlight, kunzite's colour can fade; a distinct attribute of the spodumene family. Unlike most other pink coloured stones, kunzite is often found in very large sizes. Its vitreous luster and hardness is similar to quartz, making it softer than pink sapphire and spinel.

Kunzite Origin and Gemstone Sources

Named for the mineralogist and jeweller George Frederick Kunz who first catalogued it in 1902, Kunzite is the pink to violet variety of the silicate, Spodumene. It has a glassy transparency, and forms in flattened prismatic crystals with vertical striations. It is highly pleochroic, shifting from pale pink to light violet and even colourless, depending on the angle of observation, and though its perfect cleavage makes cutting difficult, it can be faceted into beautiful gems. Kunzite was first discovered in Connecticut, USA. The first significant commercial deposit was discovered 1902 in the Pala region of San Diego, California, where morganite (pink beryl) was also discovered. The most important deposits of kunzite are from Minas Gerais, Brazil, but most of the current supply is from Afghanistan and Pakistan. Other sources include Madagascar, Myanmar and the USA. Smaller gem quality deposits have also been found in Canada, Russia, Mexico, Sweden and Western Australia.

Properties of Kunzite

Chemical FormulaLiAlSi2O6
ColourPink, Purple
Hardness6.5 - 7
Crystal SystemMonoclinic
Refractive Index1.66 - 1.68
SG3.1 - 3.2
TransparencyTransparent
Double Refraction.015
LusterVitreous
Cleavage1,2 - prismatic
Mineral ClassSpodumene

Jasper

What is Jasper?

Jasper is an opaque variety of Chalcedony, and is usually associated with brown, yellow, or reddish colours, but may be used to describe other opaque colours of Chalcedony such as dark or mottled green, orange, and black. Jasper is almost always multicoloured, with unique colour patterns and habits.
Jasper, an aggregate of microgranular quartz and/or chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in colour; and rarely blue. The common red colour is due to iron inclusions. The mineral aggregate breaks with a smooth surface and is used for ornamentation or as a gemstone. It can be highly polished and is used for vases, seals, and snuff boxes. The specific gravity of jasper is typically 2.5 to 2.9. Along with heliotrope (bloodstone), jasper (green with red spots) is one of the traditional birthstones for March. Jaspilite is a banded iron formation rock that often has distinctive bands of jasper.

History and Introduction

Jasper is one of the many gemstone varieties of quartz available today. It is an opaque and impure variety of silicon dioxide (SiO2). The name 'jasper' is derived from the Greek word for 'spotted stone', referring to its typical multicoloured, striped, spotted or flamed appearance. Jasper can form in virtually any colour. Jasper is usually considered a chalcedony, but some scientists classify jasper as a separate type because of its distinctive grainy structure.
Jasper is a dense substance, up to twenty percent of which can be made of foreign materials. Due to these trace impurities, jasper is rarely uniform. In some cases, jasper may even grow together with agate or opal. The patterns of jasper are formed during the process of mineral consolidation, determined by the exact flow and deposition of silica-rich sediments or volcanic ash. Jasper is often modified by other intruding impurities. As original deposits of silica materials naturally form with fissures and cracks after deposition, they are later filled by other minerals, such as iron oxide, manganese dioxide, metal oxide and sometimes organic matter. The final settling of these materials determines the specific appearance of the final substance.
The most common jasper patterns include interesting marbling and veining, orbital rings, streaks, spots, flaming and banding. Like agate stone, there are numerous trade names and classifications used for jasper today. The names can be very confusing, but fortunately, most are used only by the most avid collectors.

Types of jasper

Jasper is an opaque rock of virtually any colour stemming from the mineral content of the original sediments or ash. Patterns arise during the consolidation process forming flow and depositional patterns in the original silica rich sediment or volcanic ash. Hydrothermal circulation is generally thought to be required in the formation of jasper.
Jasper can be modified by the diffusion of minerals along discontinuities providing the appearance of vegetative growth, i.e., dendritic. The original materials are often fractured and/or distorted, after deposition, into diverse patterns, which are later filled in with other colourful minerals. Weathering, with time, will create intensely coloured superficial rinds.
The classification and naming of jasper varieties presents a challenge. Terms attributed to various well-defined materials includes the geographic locality where it is found, sometimes quite restricted such as "Bruneau" (a canyon) and "Lahontan" (a lake), rivers and even individual mountains; many are fanciful, such as "forest fire" or "rainbow", while others are descriptive, such as "autumn" or "porcelain". A few are designated by the place of origin such as a brown Egyptian or red African.
Picture jaspers exhibit combinations of patterns (such as banding from flow or depositional patterns (from water or wind), dendritic or colour variations) resulting in what appear to be scenes or images (on a cut section). Diffusion from a centre produces a distinctive orbicular appearance, i.e., leopard skin jasper, or linear banding from a fracture as seen in leisegang jasper. Healed, fragmented rock produces brecciated (broken) jasper. While these "picture jasper" can be found all over the world, specific colours or patterns are unique, based upon the geographic region from which they originate. Oregon's Biggs jasper, and Bruneau jasper from Bruneau Canyon near the Bruneau River in Idaho are known as particularly fine examples. Other examples can be seen at Llanddwyn Island in Wales.
The term basanite has occasionally been used to refer to a variety of jasper, a black flinty or cherty jasper found in several New England states of the US. Such varieties of jasper are also informally known as lydian stone or lydite and have been used as touchstones in testing the purity of precious metal alloys.

Identifying Jasper

Jasper is a variety of quartz with a chemical composition composed primarily of silicon dioxide. Up to 20% percent of fine dense jasper can be composed of foreign materials, typically hematite, pyrolusite, clay or calcite. It has such a distinctly grainy structure compared to other forms of chalcedony that some scientists even put jasper into its own individual group within the quartz family. Jasper has a microcrystalline structure which means its trigonal crystals can only be seen under high magnification. It can be easily distinguished from many other similar materials by its excellent hardness and lack of cleavage.

Jasper Origin and Gemstone Sources

Jasper gemstones can be found in many locations around the world. Some of the most notable deposits are sourced from Australia, Brazil, Canada, Egypt, India, Indonesia, Kazakhstan, Madagascar, Mexico, Russia, Uruguay, Venezuela and the United States of America, including Arizona, Arkansas, California, Idaho, Oregon, Texas and Washington.

Properties of Jasper

Chemical FormulaSiO2
ColourWhite, Blue, Red, Green, Yellow, Orange, Brown, Gray, Black, Banded, Multicoloured
Hardness6.5 - 7
Crystal SystemHexagonal
Refractive Index1.54 - 1.55
SG2.63 - 2.65
TransparencyOpaque
Double Refraction.009
LusterVitreous
CleavageIndiscernible
Mineral ClassQuartz (Chalcedony).