490 REPORT OF NATIONAL MUSEUM, 19(X). 



Transparent to subtransluccnt. Specific gravity, 3.27. Color, clove 

 brown, plum })luo, violet, pearl gray, and honey vellow to greenish 

 3'ello\v, It is usually strongly pleochroic, pale olive-green specimens 

 giving, with the dichroscope, olive-green and violet-blue images. 



The composition of axinite in 100 parts is approximately: Silica, 4.3; 

 boron trioxide, 5; aliunina, 16; ferric oxide, 10; manganese oxide, 3; 

 potash, 1; lime, 20; magnesia, 2. 



AZURITE AND MALACHITE. 



The use of the two carbonates of copper as gems is limited by their 

 softness and opacity. Their hardness is 4; their specific gravity varies 

 from 3.5 to 1, and they possess a vitreous to adamantine luster, 

 occasionally silky. Malachite is a bright green in color, varjdng 

 somewhat in tint and usuallj^ in veinings or markings. Azurite shows 

 the various shades of azure passing into Berlin blue. Botryoidal 

 masses of these carbonates occur in which the two minerals are in 

 alternate concentric layers, giving rise to a very pleasing effect. 



Malachite contains: Copper oxide, 71.9; carbon dioxide, 19.9; water, 

 8.2. Azurite contains: Copper oxide, 69.2; carbon dioxide, 25.6; 

 water, 5.2. (Plate 1.) 



BARITE. 



Barite can hardl}^ be regarded as a gem stone, its softness permit- 

 ting rapid abrasion. Its hardness does not exceed 3.5; its specific 

 gravit}' is 4.3 to 4.7, depending upon the amount of impurity present. 

 Its color ranges between white, gray, blue, red, or brown; the colors 

 occasionally banded or mottled. Luster vitreous, sometimes pearly. 



One hundred parts contain: Baryta, 65.59; sulphuric acid, 34.33. 



BERYL. 



EMERALD AQUAMARINE— GOSHENITE. 



The beryl crystallizes in six-sided hexagonal prisms, usually long- 

 prismatic and often having the prism faces more or less deeply 

 striated vertically. The specific gravity of the transparent fiawless 

 beryl is 2.73; usually 2.69 to 2.70. Hardness 7.5 to 8. Brittle. 

 Cleavage indistinct. Fracture uneven to conchoidal. Luster vitre- 

 ous, occasionally resinous. The colors of the beryl include emerald 

 green passing into pale green, and pale blue, pale 3'ellow, honey, wine, 

 and citrine yellow, white, to a pale rose-red. The pleochroism is 

 more or less distinct; occasionally strong, especially in the emerald 

 which, when viewed across the prism with the dichroscope, shows two 

 different shades of green. 



Mineralogically the })eryl includes the emerald, aquamarine, 

 goshenite, and davidsonite. The general composition, fundamental 

 crystalline form, hardness, and specific gravity of all the varieties are 

 essentially the same, the difference being primarily one of color. The 



