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NEW YORK STATE MUSEUM 



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

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

 twinning, which is characteristic of this group of carbonates, 

 produces prismatic forms which somewhat resemble hexagonal 

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

 corallike forms (pi. SJ 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 oalcite 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. 



