Emerald

Emerald is the green variety of beryl with a chemical composition of Be3Al2Si6 O18. This beryllium aluminium silicate frequently has some sodium, lithium, and cesium included in the mineral ( Chesterman, 1979, p.560). The luster is vitreous and beryl has a colorless streak. The hardness is 7.5-8 and specific gravity ranges from 2.66 to 2.92. Beryl's fracture is uneven to conchoidal and the cleavage is indistinct in one direction. Gem quality stones are transparent to translucent. The crystals are hexagonal and are usually six sided prisms that are striated lengthwise. The natural emerald is noted for its deep green color and the presence of inclusions verify its natural origin. Colors for beryl include blue-greenish blue (aquamarine), yellow (golden beryl), light yellow green (heliodor), red (bixbite), pink or peach (morganite), colorless (goshenite), as well as the bright green emerald, which is considered the most valued of these varieties. Beryl develops in pegmatites and certain metamorphic rocks. Fine emeralds have velvety body appearance and the value is in the even distribution of color. Beryl can also have a pale green variety that is not gem quality and this mineral occurs with scheelite in a pegmatite near Oreana, Pershing Co. Nevada as well as in North Carolina, Colorado and California (Chesterman, 1979, p. 560-563).