Category: Gem Notes

Diopside

Introduction Diopside is a mineral species crystallizing in the monoclinic crystal system with the formula CaMgSi2O6. It is the end member of a solid solution series to hedenbergite where the magnesium is replaced by iron, CaFeSi2O6. There are a few intermediate…

Prehnite

Introduction Prehnite is a mineral, well known to collectors, with the formula Ca2Al2Si3O10(OH)2. Crystals are rare, typically forming with stalactitic or botryoidal habit (Fig. 1). It is not commonly seen in jewelry stores but is occasionally…

Apatite

Introduction Apatite is a group of closely related species, namely fluorapatite Ca5(PO4)3F, chlorapatite Ca5(PO4)3Cl, and hydroxylapatite Ca5(PO4)3(OH). Fluorapatite is by far the most common species of the apatite group. Almost all gemstones are fluorapatite although rarely…

Fluorite

Introduction & History Fluorite is calcium fluoride (CaF2). It is well known in the mineralogical world and is often seen as well-formed crystals or crystal groups. Fluorite’s low durability has lessened its importance in the world…

Benitoite

Introduction and History: Benitoite is barium titanium silicate, BaTi(Si3O9). Mindat.org lists several localities for benitoite including the Czech Republic, Japan, Arkansas and Montana, but it is well known that the only source of gem quality…

Tugtupite

Introduction: Tugtupite is an interesting and rarely seen gem, closely related to sodalite with the formula, Na4(AlBeSi4O12)Cl. It was discovered in 1957 by Professor H. Sørensen in the coastal cliffs of Tugtup Agtakôrfia on the…

Ethiopian Opal

Since reemerging in the market after a decade long hiatus, opal from Ethiopia has generated a lot of buzz during the past six years. Anyone visiting a major gem show since 2009 has likely seen…

Vesuvianite

Introduction: Vesuvianite is a tetragonal mineral with the formula Ca10Mg2Al4(SiO4)5(Si2O7)2(OH)4. As the name implies, it was named after the locality of its discovery, Mount Vesuvius, Campania, Italy. It has an interesting history in the nomenclature…

Sphalerite

Introduction: Sphalerite is zinc sulfide (ZnS), also known as zinc blende. It is a fairly common mineral crystallizing in the isometric system and is a principal ore of zinc. In addition, it often contains iron…

Gem Note: Hauyne

Introduction: Haüyne is an extremey rare mineral, a member of the sodalite group, and is even more rare as a gemstone with the formula (Na,Ca)4-8Al6Si6(O,S)24(SO4,CL)1-2. It is sometimes seen in the literature as hauyne or…