GEMSTONES, SEMI-PRECIOUS STONES, LAPIDARY MATERIALS, ORNAMENTAL STONES, AND OTHER UNIQUE MINERALS AND ROCKS OF WYOMING

There are several unique mineral and rock localities in Wyoming. Some of these include diamond, cordierite, olivine, varisite, corundum, komatiite, kimberlite, lamproite, jade, and many other rocks and minerals. One of the more unusual rocks is a group of ultrapotassic volcanic rocks in the Leucite Hills, known as lamproite. The unique mineral assemblage includes phlogopite, olivine, leucite, sanidine, potassium-richterite, diopside, apatite, anacite, spinel, priderite, wadeite, perovskite, shcherbakovite, and armalcolite. Some olivine associated with these rocks is semi-precious peridot. Another rare potassic rock, kimberlite, occurs in southeastern Wyoming. Some of these hybrid peridotite breccias contain chromian diopside, chromian enstatite, pyrope garnet, and diamond. A few kimberlites have yielded gem- and industrial-quality diamonds (micros to 28.3 cts). Corundum is associated with some Precambrian vermiculites. Other hosts include quartzofeldspathic gneiss and serpentinite. Large corundum specimens and fuchsite pseudomorphs after corundum were recently found in the Granite Mountains. Another locality in the Laramie Range, transparent sapphire-blue cordierite (iolite) and transparent corundum were recently discovered. Fashioned corundum yielded pink, reddish-pink, and pinkish-brown sapphires weighing 0.75, 1.15, 1.47, 2.0 and 3.0 cts. Specimens of transparent to translucent cordierite grains and nodules range from 1.5 to >3000 cts. The first stones fashioned produced iolites weighing 0.5, 1.0 and 1.49 cts, and two translucent to opaque ornamental cordierites (3.4 & 3.9 cts). Nephrite jade, produced by metasomatic alteration of amphibolite during regional metamorphism in central Wyoming was accompanied by distinct wallrock alteration assemblage of mottled pink and white gneiss by secondary clinozoisite, pink zoisite, pistachio-green epidote, green chlorite, and white sericite. Wyoming is also a source for a variety of jaspers and agates, aquamarine, gold nuggets and other potentially valuable minerals and rocks.