ANDESINE
ANDESINE See “PLAGIOCLASE”
ANORTITE
ANORTITE See “PLAGIOCLASE”
ALBITE
ALBITE Introduction See “PLAGIOCLASE”
AMBER
AMBER Amber is a low-density amorphous fossil plant resin, used since the Neolithic times as a gemstone and still reaching very high prices due to the huge demand created by the Chinese market. The color of amber varies from very light yellow to honey and black. There is amber from the Dominican Republic that is […]
ANATASE
ANATASE Anatase -TiO2 – is a relatively common oxide. It occurs as an accessory mineral in many igneous and metamorphic rocks and easily goes unnoticed. It does not constitute an ore. Anatase is one of the five polymorphs of titanium oxide found in nature. The most common are brookite and rutile. Anatase may contain V, Nb, […]
ARSENOPYRITE
ARSENOPYRITE Arsenopyrite – FeAsS – is a very common sulfide and constitutes an ore of As, but As is usually recovered as a by-product processing ores of other elements. Arsenopyrite has a high content (46%) in As and a turbulent history of exploration, with over 40 names currently discredited. May contain high levels of Au. […]
ALGODONITE
ALGODONITE Algodonite is a rare arsenide that integrates complex ores of Cu and Ag with As.It may contain Ag, and there is a synthetic variety with Ag.In older literature, there is a differentiation between α-algodonite and β-algodonite. Similarly, domeykite, which occurs in association, was “subdivided” into α-domeykite, β-domeykite, and γ-domeykite. Some references even mention δ-forms, […]
APOPHYLLITE
APOPHYLLITE Apophyllite is a relatively common phyllosilicate, typically a secondary mineral associated with basic igneous rocks. It does not constitute ore, but it has acceptance among collectors. For decades there has been collection and commercialization of pieces with apophyllite in India, in the basaltic rocks of the “Traps” of the Deccan. In reality, “apophyllite” is […]
APATITE
APATITE “Apatite” – (Ca5(PO4))3(F,OH,Cl) – is not a mineral, but a term used for members of a group of isomorphic minerals formed by apatite-(CaF) (very common), apatite-(CaOH) (much less common, forms teeth and bones) and apatite -(CaCl) (very rare). In hand samples they are practically indistinguishable and each one can partially replace the others. These […]
ANTHOPHYLLITE
ANTHOPHYLLITE Anthophyllite – ☐{Mg2}{Mg5}(Si8O22)(OH) – is an inosilicate of the Amphibole Supergroup. It is a rarer amphibole, typical of medium to high grade metamorphic rocks. Anthophyllite with a fibrous habit is one of the six minerals known as “asbestos” and was mined in some locations until the 1970s, when mines were closed due to problems […]