Hambergite, named after Axel Hamberg, the Swedish mineralogist, occurs as colourless to yellowish white crystals, but is rarely gem-quality. Brittle, with perfect cleavage, it's very fragile and suitable just for collectors. When cut, it appears like glass, but double images of the rear facets might be seen with the table facet because of its high birefringence.
Gem quality hambergite can be found in Kashmir (India), as well as in Madagascar.
Several types of gypsum are utilized as decorative stones. The most crucial, alabaster, is located as fine-grained masses in pastel shades, but is often stained in stronger colours. Selenite is colourless, occasionally cut for collectors, but very soft. Satin spar is really a fibrous variety, polished or cut “en cabochon”. Rose shapes (called "desert rose") also occur.
Localities include Italy and England (Alabaster), Italy, Mexico, the United States and Chile (Selenite).
Cerussite is generally colourless, but white, grey, and black specimens have been discovered. Its two most distinctive features are its high density and it is adamantine lustre. Crystals possess a stubby tabular or elongate habit. Although attractive, it's too soft to possess much value like a gemstone, and it is cut solely for collectors. Cerussite is generally found around lead ores. Large, clear, transparent, colourless, cuttable crystals have been discovered in Tsumeb (Namibia). Other localities include Austria, Australia, Czechoslovakia, the united states, Germany, Scotland, and Italy, including Sardinia. Sometimes wrongly identified as diamond along with other colourless gems, it might be distinguished by its higher density.
Celestine is generally found as colourless, milky white, yellow, orange or pale blue prismatic crystals or perhaps in fine-grained masses. Having a hardness of only 3.5 on Moh’s scale and perfect cleavage, Celestine is very fragile. It's been cut for that collector, however, plus some fine specimens are visible in museums. Celestine may occur with sandstones or limestones, in evaporate deposits, in pegmatites, in cavities in volcanic rocks, or with galena and sphalerite in mineral veins. The majority of the material that's able to be faceted can be found in either Namibia or Madagascar. It's also present in Italy (including Sicily), England, Czechoslovakia, the united states, and Canada.
Cassiterite is the principal ore of tin. It is usually recovered from mines as black opaque grains, which are of little use in jewellery. Crystals are generally short, stubby prisms. Occasionally, rare, transparent, reddish brown crystals with adamantine lustre are found and faceted for collectors. They could be confused with diamond, brown zircon, and sphene, but for the higher specific gravity and distinct dichroism. Cassiterite occurs in pegmatites and can be washed into alluvial deposits. Localities include the Malay Peninsula, England, Germany, Australia, Bolivia, Mexico and Namibia. The name “cassiterite” comes from the Greek word, kassiteros, meaning tin.
Calcite is a mineral named after its calcium content. It is one of the most common minerals found in abundance on the Earth. Iceland spar is a colorless variety of calcite, which is well known for its very strong doubling (double refraction). Due to the low hardness of calcite it is not sought as gem quality mineral as it is prone to scratch but still it is used as cabochons, facetted cuts and carvings in gem industry while it is also used in production of lime which is further used in steel and glass industry. The iridescent effect seen at cleavage cracks of calcite is also popularly known as rainbow effect in trade. Common worldwide, calcite may be the principal element of limestones and marbles, as well as most stalactites and stalagmites. It is also found as large, transparent, colourless, complex crystals, or as prismatic crystals Intergrown with other minerals. Due to the softness it is simply faceted for that collector, but marbles and brown, banded calcite from limestone caves are generally employed for decoration and carving. Italy is known for high-quality marbles, particularly the creamy Carrara marble. Transparent, colourless rhombs are classified as “Iceland spar”; a white fibrous variety, cut en cabochon, shows the cat’s-eye effect. Pink and green crystals occur in the united states, Germany, and England. Calcite roughs are found in rhombohedron forms but due its perfect three directional rhombohedral cleavage and low hardness the calcite rough is cleaved within the ore or during the mining process, and does not show a complete rhombohedron. But while carefully examining it still can be figured out on a whole as a rhombohedron form.
Formation of Calcite
It is calcite (calc - calk) that has been dissolved by the acidity in rain/water passing through limestone. It then drips from cave roofs and forms calcite straws which often become blocked and then form stalactites as the calcite forms around the outside of the straw. The water dripping from the straw or stalactite deposits calcite on the floor which becomes a stalagmite or flowstone if it runs at an angle. The red in the calcite is due to ironstone in that area.
Brazilianite is an uncommon and unusual gemstone. Cut for collectors only, its yellow or yellowish green colour is nonetheless striking. Crystals are fragile and brittle, with conchoidal fracture and perfect cleavage perpendicular for their length. The primary localities have been in Brazil, where crystals as much as 15cm (6 inches) have been discovered. Smaller crystals happen to be mined in Nh in the united states. Present in Minas Gerais in Brazil in the mid 1940s, brazilianite was initially regarded as chrysoberyl, but closer examination revealed that it is a brand-new mineral. It had been named following the country by which it had been found, but has since been wrongly identified as chrysoberyl, beryl and topaz.
Beryllonite crystals are colourless, white or pale yellow, nevertheless its weak fire and low dispersion turn it into a dull gemstone. Additionally, its softness, perfect cleavage, and brittle fracture allow it to be fragile, although carefully it might be faceted for collectors. Beryllonite is really a pegmatite mineral, found linked to the minerals phenakite and berylin in Mane in the United States. It's also present in Finland and Zimbabwe, but remains an uncommon gem. Beryllonite is known as following the beryllium content in the chemical composition. It's been wrongly identified as other colourless gemstones of low dispersion.
In the 19th century the preferred colour for aquamarine was sea-green, and indeed the name itself means sea water. Today, the most valued colours are sky-blue and dark blue. Aquamarine is dichroic, appearing blue or colourless as the stone is viewed from different angles. Gem-quality aquamarine is found as hexagonal crystals, which may be up to 1m long and flawless, with striations along the length of the crystal. Aquamarine is often cut with the table facet parallel to the length of the crystal in order to emphasize the deepest coloration. The best of the gem-quality aquamarine is found in Brazil, where it occurs in pegmatites and alluvial deposits of gravel, locally called cascalho. Other localities include the Urals (Russia), Afghanistan, Pakistan, India and more recently exploited, Nigeria. A dark blue variety occurs in Madagascar. Almost all aquamarine in the market has been heat-treated to enhance its colour. Care must be taken not to overheat the stones, as they may become colourless.
Emerald derives its beautiful green colour from the presence of chromium and vanadium. Emeralds are rarely flawless, so stones are often oiled to fill and disguise cracks, hide flaws, and enhance colour. To minimize the loss of material, the step-cut (or “emerald-cut”, as it is known) is commonly used, but ancient engravings are known, and cameos, intaglios, and beads can make the best of a flawed stone. Found in granites, pegmatites, and schists, as well as alluvial deposits, the finest emeralds are from Colombia. Other sources are Austria, India, Australia, Brazil, South Africa, Egypt, the USA, Norway, Pakistan and Zimbabwe. Most emeralds used in historical jewellery would have been from Cleopatra’s mines in Egypt, which now yield only poor-quality emeralds.
Goshenite is the pure, colourless variety of beryl. It has been used to imitate diamond or emerald, by placing silver or green-coloured metal foil behind a cut goshenite gemstone, then placing the stone in a closed setting so that the foil cannot be detected. Goshenite is named after Goshen, Massachusetts, in the USA, where it was first found. Present localities include Canada, Brazil and the former USSR. Pale and colourless beryl was once used for the lenses in spectacles, thus the German word for spectacles, brille, may have been derived from the word “beryl”.
Heliodor, a yellow or golden yellow form of beryl, has always been linked with the Sun. Gem-quality specimens are occasionally found, but more usually inclusions of fine, slender tubes are present which are visible to the naked eye. Heliodor is found associated with aquamarine in granitic pegmatites. The best-quality stones are found in the Urals (Russia). Brazilian heliodor is often a pale yellow and is step-cut to give depth of colour. Heliodor from Madagascar is a finer colour. Other localities include the Ukraine, Namibia, and the USA.
Coloured by manganese impurities, the pink, rose, peach and violet varieties of beryl are called morganite after the American banker and gem enthusiast, J. Pierpoint Morgan. Morganite tends to occur as short and stubby (tabular) prisms and is dichroic showing either two shades of the body colour, or one shade and colourless. The first morganite to be described was a pale rose-coloured specimen from California (USA), where it occurred with tourmaline. Some of the finest morganite is from Madagascar; Brazil produces pure pink crystals, as well as some containing aquamarine and morganite in the same crystal. Other localities include Elba (Italy), Mozambique, Namibia, Zimbabwe and Pakistan (recently discovered). Stones with a yellow or orange tinge may be heat-treated for a purer pink.
Very rare and seldom seen as a cut stone, red beryl nonetheless has an unusually intense colour due to the presence of manganese. Found in rhyolites in the Thomas Mountains and Wah Wah Mountains in Utah in the USA. Red beryl is also called bixbite (not to be confused with bixbyite, a manganese-iron oxide).
The blue crystals of benitoite were only discovered in 1906, by a mineral prospector who mistook them for sapphires. Crystals are shaped like flattened triangles, and have a strong dispersion similar to diamond, but this is masked by the colour. Dichroism is strong: the stone appears blue or colourless when viewed from different angles. Colourless crystals occur, but are rarely faceted. Crystals occur in veins in blue schists. The sole source is in San Benito County, California (USA), after which the stone is named.
Baryte occurs in a number of colours, including colourless, white, yellow and blue, nevertheless its softness, perfect cleavage, brittleness and high density allow it to be of little use like a gemstone, which is cut for collectors only. Crystals vary a good deal and could be transparent to opaque, with a number of habits from tabular to massive. Baryte is often present in lead and silver mines. Additionally, it happens in limestones, and could be deposited by hot springs. Crystals as much as 1m (40 inches) long have been discovered in Cumbria, Cornwall, and Derbyshire in England. Other good localities include Czechoslovakia, Romania, Germany, the United States and Italy.
Azurite is definitely an azure-blue copper mineral, occasionally found as prismatic crystals (rarely faceted), but more usually in massive form Intergrown with malachite. Found specifically in copper-mining areas for example Australia, Chile, the first kind USSR, Africa, and China. Stones from Chessy, near lyons in France are known as chessylite.
