SAPPHIRINE
SAPPHIRINE Sapphirine – Mg4(Mg3Al8)O4(Si3Al9O20) – is a very rare inosilicate that occurs only in a few very specific geological situations. It has economic importance only as a gemstone and collector’s mineral. Macroscopically, it is very similar to serendibite (Ca2(Mg;Al)6(Si;Al;B)6O20), an extremely rare inosilicate. Sapphrine belongs to the Sapphirine Group, has two polytypes and two varieties […]
SMITHSONITE
SMITHSONITE Smithsonite – ZnCO3 – is a relatively common carbonate that often occurs as part of a mixture of Zn ore minerals called “calamine” in the mining industry. It could be a Cd ore. “Calamine” is not a mineral, but a term for a mixture of smithsonite and hemimorphite, which are identical in hand sample; […]
SPINEL
SPINEL Spinel – MgAl2O4 – is a common oxide that occurs mainly as an accessory mineral of igneous rocks. It has economic importance only as a gemstone, imitating ruby (red corundum) and sapphire (blue corundum). Synthetic spinel in sheets resembles glass, but has much greater strength. The spinel belongs to the Spinel Group and forms […]
SIDERITE
SIDERITE Siderite – FeCO3 – is a rarer carbonate of the Calcite Group, typical of hydrothermal veins with metals and an important historical iron ore, with 48% iron, no S or P, but some Mg, Mn, Ca, Zn and Co. It supplies a superior quality steel, already recognized by the Romans as “ferrum nordicum”. Its […]
SPHALERITE
SPHALERITE Sphalerite (old names: “blende”, “zinc blende”) – ZnS – is a common sulfide and the main ore of Zn. May constitute a Cd ore. Sphalerite is usually massive. Crystals are rare, tetrahedral and dodecahedral, typically very complex and distorted (conical and curved faces); can look like octahedrons, reach 30 cm. Crystals show strong brilliance […]
STILPNOMELANE
STILPNOMELANE Stilpnomelane – (K,Ca,Na)(Fe,Mg,Al)8(Si,Al)12(O,OH)36·nH2O – is a rarer phyllosilicate. It does not constitute ore. It is classified in the Stilpnomelane Group and is isostructural with franklinphilite, parsettensite and chalcodite. It has three varieties. Under the microscope, the optical properties vary depending on varying degrees of the Fe oxidation state; distinguishes between ferro-stilpnomelan and ferri-stilpnomelan. Macroscopically […]
SULPHUR
SULPHUR Sulphur – S8 – is a relatively common native element, characteristic of various geological environments. The mineral is written “sulphur”; the commodity is written “sulfur”. Sulphur is an important mineral, as sulfur has many industrial applications. Sulphur is classified in the Sulphur Group and is a polymorph of rosickyite (monoclinic S, very rare) and […]
SCAPOLITE
SCAPOLITE Scapolite – (Na,Ca,K)4Al3-6Si9-6O24(Cl,CO3,SO4) – is a rarer tectosilicate, characteristic of some specific geological situations. It is unimportant as an ore, but some varieties are used as gemstones. “Scapolite” is not a mineral, but a generic term referring to the members that make up the series between marialite (of Na) and meionite (of Ca), classified […]
SODALITE
SODALITE Sodalite – Na8Al6Si6O24Cl2 – is a feldspathoid, a tectosilicate of more restricted occurrence, occurring in rocks undersaturated in silica. When blue, it constitutes rocks of high commercial value, such as “Granito Azul Bahia” (which is not granite, of course). It is classified in the Sodalite Group. May contain K, Ca, Fe, Mn, Br, S […]
SPODUMENE
SPODUMENE Spodumene – LiAlSi2O6 – is a rare inosilicate, characteristic of lithium-bearing pegmatites. It is the main mineral in hard rock Li ores. Lithium can be mined in brines or hard rock mines, which are mines located in pegmatites exploiting spodumene, lepidolite, petalite, and other minerals containing Li. Spodumene is classified in the Pyroxene Group, […]