ANHYDRITE
ANHYDRITE Anhydrite – CaSO4 – is a very common anhydrous sulfate, an important constituent of evaporitic sequences and related deposits. It is a very important ore. Anhydrite is usually very pure, but may contain Sr and Ba. It has fusibility 2 (melts in the candle flame). Anhydrite crystals reach 15 cm in length, with 40 […]
ANDALUSITE
ANDALUSITE Andalusite – Al2SiO5 – is a relatively common nesosilicate, characteristic of some types of metamorphic rocks. It could be used as a raw material for silico-aluminous refractories, but seldom occurs in economically viable volumes. It is one of the polymorphs of the Al2SiO5 Group: kyanite, sillimanite and andalusite. Forms a series with kanonaite (Mn3+Al(SiO4)O). […]
ANALCIME
ANALCIME Analcime – Na2(Al2Si4O12).2H2O – is a tectosilicate from the Zeolite Group. It is a relatively rare mineral, commonly found in association with other zeolites. It has no economic importance others than the market for mineral collectors. The chemistry and structure of analcime are more similar to those of feldspathoids. It is cubic/pseudocubic, but can […]
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 […]
ALUNITE
ALUNITE Alunite – KAl3(SO4)2(OH)6 – is a relatively common sulfate, mined as a source of alum (KAl(SO4)2-12H2O), as an ore of Al (36.92% Al2O3) and K (11.37% K2O) or as a raw material for potassium fertilizers. It is a traditional and important ore in certain regions, as alunite occurrences are very common; some deposits are […]
ALLANITE
ALLANITE Allanites – (Ca,Mn,Ce,Y,Th,La)2(Fe,Ti,Al)3O(Si2O7)(SiO4)(OH) – are relatively common sorosilicates that constitute ore of Rare Earth Elements (REEs), as they can contain up to 20% of them. In reality, “allanite” does not designate a mineral, but is just a generic name for the minerals that make up the Allanite Group, classified in the Epidote Supergroup. Based […]
AENIGMATITE
AENIGMATITE Aenigmatite – Na4[Fe2+10Ti2]O4[Si12O36] – is a very rare inosilicate similar to amphiboles (same habits). It has no economic importance. It is classified in the Sapphirine Supergroup, Aenigmatite Group, forming a series with wilkinsonite. May contain Mn, Mg, Ca, K, Cl and Al as impurities. Aenigmatite is related to malakhovite. 1. Characteristics Crystal system: Triclinic […]
AEGIRINE-AUGITE
AEGIRINE-AUGITE Aegirine-augite is an inosilicate of the Pyroxene Group. It is a rarer mineral, typical mainly of some alkaline igneous rocks. It has no importance as an ore. It is not considered a mineral species, but only an intermediate term between aegirine and augite, which form a series in the Pyroxene Group, Clinopyroxene Subgroup. For […]
AEGIRINE
AEGIRINE Aegirine is an inosilicate of the Pyroxene Supergroup. It is an uncommon mineral, whose occurrence is restricted to some types of rocks. It has no economic importance. Aegirine forms a solid solution with augite. The middle term is aegirine-augite. “Acmite” was a term used for both green and brown aegirines with pointed ends; the […]
ACANTHITE
ACANTHITE Acanthite – Ag2S – is a rarer sulfide typical of hydrothermal veins. It is the most important silver ore after argentiferous galena. Acanthite and argentite are polymorphs. Silver sulfide can form at more than 177ºC (literature diverges: 173ºC, 179ºC, 180ºC) with cubic structure or below this temperature with monoclinic structure. The mineral with a […]