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Common examples include: serpentine group, actinolite, kyanite, gypsum, nitratine, tremolite (i.e. asbestos) Asbestiform is a crystal habit. It describes a mineral that grows in a fibrous aggregate of high tensile strength, flexible, long, and thin crystals that readily separate. The most common asbestiform mineral is chrysotile, commonly called “white asbestos“, a magnesium phyllosilicate part of the serpentine group. Other asbestiform minerals include riebeckite,Continue Reading

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Acicular, in mineralogy, refers to a crystal habit composed of slender, needle-like crystals. Crystals with this habit tend to be fragile. Complete, undamaged acicular specimens are uncommon. The term “acicular” derives from the Late Latin “acicula” meaning “little needle”. Strictly speaking, the word refers to a growth habit that is slender and tapering to a point. PrismaticContinue Reading

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Oltu stone (Turkish: Oltu taşı) is a kind of jet found in the region around Oltu town within Erzurum Province, eastern Turkey. The organic substance is used as semi-precious gemstone in manufacturing jewellery. Location and extraction Oltu stone, sometimes called also “Erzurum stone”, is principally mined in the villages northeast of Oltu town, around Tutlu Dağı (Yasak Dağ) as wellContinue Reading

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Jet is a type of lignite, the lowest rank of coal, and is a gemstone. Unlike many gemstones, jet is not a mineral, but is rather a mineraloid. It is derived from wood that has changed under extreme pressure. The English noun jet derives from the French word for the same material, jaiet (modern French jais), ultimately referring to the ancient town of Gagae. Jet is eitherContinue Reading

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Wood opal is a form of petrified wood which has developed an opalescent sheen or, more rarely, where the wood has been completely replaced by opal. Other names for this opalized sheen-like wood are opalized wood and opalized petrified wood. It is often used as a gemstone. ReferencesContinue Reading

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Petrified wood, also known as petrified tree (from Ancient Greek πέτρα meaning ‘rock’ or ‘stone’; literally ‘wood turned into stone’), is the name given to a special type of fossilized wood, the fossilized remains of terrestrial vegetation. Petrifaction is the result of a tree or tree-like plants having been replaced by stone via a mineralization process that often includes permineralization and replacement.  The organic materials making upContinue Reading