Prehnite

Posted on February 27, 2016 by John J. Bradshaw, GG (GIA)

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…

Gem Notes

Apatite

Posted on December 29, 2015 by John J. Bradshaw, GG (GIA)

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…

Gem Notes

Fluorite

Posted on November 2, 2015 by John J. Bradshaw, GG (GIA)

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…

Gem Notes

Benitoite

Posted on August 31, 2015 by John J. Bradshaw, GG (GIA)

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…

Gem Notes

Tugtupite

Posted on June 30, 2015 by John Bradshaw, GG (GIA)

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…

Gem Notes

Ethiopian Opal

Posted on May 1, 2015 by The Gemworld Staff

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…

Gem Notes

Vesuvianite

Posted on May 1, 2015 by John Bradshaw, GG (GIA)

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…

Gem Notes

Sphalerite

Posted on March 3, 2015 by John Bradshaw GG (GIA)

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 Notes

Gem Note: Hauyne

Posted on January 7, 2015 by John Bradshaw GG (GIA)

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…

Gem Notes

Serendibite

Posted on November 3, 2014 by John Bradshaw GG (GIA)

Introduction: Serendibite is an extremely rare mineral with the chemical formula Ca2(Mg,Al)6(Si,Al,B)6O20. The mineral was first discovered in 1902 by G.T. Prior and A.K. Coomaraswamy at Gangapitiya, which is near Ambakotte, approximately 12 miles (20 km…

Gem Notes