CAKHONATKS 



..-_>_' 1:1: .7205 ; 100 A 1 10 = 31 54' ; 001 A 101 = 49 10' 

 001 A Oil = 35 46' 30"; Common forms, c(011), b(010), 

 m ( 1 10), o (112), other forms numerous hut not common ; Twinning 

 plane, 110, often repeated; 

 Brittle, fracture subcon- 

 choi.lal; H. =3.54; G. = 2. 

 93-2.95; Color, white, 

 yellow, gray, sometimes 

 green ; Streak, white; 

 Luster, vitreous ; Trans- 

 parent to opaque; a = 

 p = 1.681; <y = 1.685; 



Flo. 449. Aragonite from Herrengrund, Hun- 

 gary. 



y a = .156; Optically 

 (-); 2V = 18 11'; Axial 

 plane parallel to 100; Bx :l 

 parallel to c. 



B.B. Like calcite. 



General description. 



Crystalline habit prismatic, 

 combinations of the unit 

 prism with the brachy- 

 pinacoid; as the prism angle is 116 12', the crystals have a 

 hexagonal outline. Such combinations terminated by the base 

 are common at Herrengrund, Hungary. At Cleator, England, 

 crystals occur illustrating the chisel-shaped habit, where the ter- 

 mination is formed by the long steep pyramid (991) and dome 

 (091), in which the dome predominates, giving the crystal the 

 flattened or chisel appearance. Twinning in aragonite adds to 

 the hexagonal appearance, as the composition plane is parallel to 

 the unit prism ; when repeated and joined in parallel position, 

 yield short stout hexagonal prisms terminated by a flat face, the 

 !>a-e. The complexity of such specimens is easily seen by the 

 striations on the base, or by the concave or offset prism faces. 



Aragonite, as the unstable form of calcium carbonate at ordinary 

 temperatures, is less common than calcite. It is formed from hot 

 solutions, around thermal springs, in crusts, botryoidal shapes, and 

 peculiar coral-like masses known as "flos-ferri/ ' or flowers of iron, from 

 their form and association with beds of iron ore. The " sprudelstein" 

 of the hot springs of Carlsbad, Bohemia, is aragonite, as well as the 

 calcic skeleton of corals and the pearly lining of many shells. 



