Especially since World War II, the pegmatites of the state of Minas Gerais have yielded some of the world's finest specimens of topaz, chrysoberyl, euclase, elbaite, and beryl (in all of its colored varieties); phosphate-rich pegmatites of the same state have furnished the world's finest specimens of brazilianite, beryllonite, eosphorite, hydroxylherderite, amblygonite and more; complex pegmatites of other kinds have provided cassiterite, xenotime, monazite and several rare-earth species; Brazilian specimens of titanite, phenakite, fluorapatite, kyanite, scheelite, spessartine and bertrandite
are among the world's very best.
About 60% of world production is from bertrandite
The Warm Springs deposit, discovered in the early '60s, is a hydrothermally altered rhyolite, mineralized with bertrandite
, grading from .
Other minerals found in the Kafubu emerald area include allanite (small euhedral crystals in rock), amethystine quartz (in a single 10-cm-wide vein), bertrandite
(7-mm crystal aggregates replacing beryl), columbite-(Mn), tantalite-(Mn) (prismatic euhedral microcrystals), monazite (euhedral microcrystals), epidote, gahnite, phenakite (crystals to 1 cm enclosed in beryl), plumbomicrolite (brownish yellow crystals to 1 mm), and xenotime (euhedral micro-crystal inclusions) (Seifert et al.
The main source of beryllium in the United States is bertrandite
Ever since then, intrepid collectors have been finding attractive aquamarine specimens (many of gem quality), as well as the associated secondary beryllium minerals phenakite and bertrandite
, at elevations above 12,000 feet on the steep, rocky slopes of the mountain.
In addition to the finest "royal purple" fluorapatites in the world, the Pulsifer Quarry has produced world-class bertrandite
, gahnite, and manganotantalite crystals.
The discovery of aquamarine was soon followed by the recognition of phenakite, bertrandite
, fluorite and topaz from the Mount Antero and Mount White areas.
Important subordinate species include muscovite, calcite, and zeolites (especially stilbite); occasionally, rutile, fluorapatite, titanite, phenakite, bertrandite
and rare-earth-element species are found in the clefts, in nearly all cases as microcrystals (Parker, 1973; Amacher, 1982; Graeser, 1998).
Associated collectable minerals including beryl (aquamarine), green fluorite, phenakite and bertrandite
have also been found there.
For the mineral collector there was an unusually fine selection of good minerals at the Show: vanadinite from the Ramsey mine, La Paz County, Arizona; lovely transparent green vivianite from Oruro, Bolivia; malachite crystals from the Mashamba West mine, Zaire; uvite from Brumado, Brazil; sparkling white bertrandite
clusters from Conselheiro Pena, Brazil; big orange scheelite crystals from Hunan, China; diamond crystals from China; gemmy green zoisites from Pakistan; azurites from Morenci, Arizona; and, from Mexico, some wonderful snow-white Santa Eulalia hemimorphite and small, deep green ludlamites.
He studied various Minas Gerais pegmatites, including especially those near Linopolis and Galileia, and also the Golconda mine (from which he recovered the world's finest bertrandite