84 



NEW YORK STATE MUSEUM 



uiatic in habit (fig. 200) with acute terminations (domes and pyra- 

 mids) which merge into radiating needlelike forms (pi, 26 2 ). A 

 twinning, which is characteristic of this group of carbonates, 

 produces prismatic forms which somewhat resemble hexagonal 

 prisms (fig. 201, pi. 27J. Stalactitic incrusfing, columnar and 

 corallike forms (pi. S A ) also occur. The prevailing color is white, 



Fig. 200 Fig. 201 



Aragonite 



which shades to violet, yellow and pale green in some varieties; 

 the luster is vitreous. 



Crystallized varieties may be distinguished from calcite by 

 the difference in form but massive specimens can only be deter- 

 mined by cleavage and optical tests. Aragonite is formed in 

 much the same way as calcite, but is of far less common occur- 

 rence. It is often found associated with gypsum and serpentine 

 and with iron ore as flos ferri (pi. 8J. In the United States 

 aragonite is found in several localities in California, in Connecti- 

 cut, Illinois, Missouri, New Mexico and Pennsylvania and in 

 Niagara, Orange and Madison counties, N. Y. 



Witherite BaC0 3 



Witherite is a barium carbonate containing 22.3^ carbon 

 dioxid and 77.7$ baryta. 



Though witherite is orthorhombric in crystallization single 

 crystals are practically unknown; twinned forms resembling 

 a series of hexagonal pyramids superposed are characteristic 

 (pi. 27 2 ). It also occurs massive in columnar or granular 

 structure. The luster is vitreous and the color white, gray or 

 yellowish. 



