Rogers. | Minerals of the Galena-Joplin District. 493 
Malachite. 
Composition, hydrous copper carbonate, CuCOs,Cu(OH)s: Cu, 57-52%; C, 
5-43%; H, 0-90%; O, 86:20%. Hardness, 3-5-4; gravity, 3-9-4; color, bright 
green; crystallization, monoclinic; cleavage, basal, highly perfect, clino- 
diagonal, less distinct; angle, B=61° 50’. 
Malachite is never observed here in crystals but always as a 
massive material, sometimes fibrous crystalline in structure. 
It is widely distributed throughout the district and is com- 
monly associated with other copper minerals. Occasionally 
it is found as a thin coating on chalcopyrite crystals. At the 
Big Coon mine, at Galena, it surrounds massive cuprite, evi- 
dently being formed from the latter. It also coats the covel- 
lite pseudomorphs after sphalerite found at the same mine. 
. Azurite. 
Composition, 2CuCOs, Cu(OH )2: Cu, 56-65%; C, 7-19%; H, 0-60%; O, 
35-28%. Hardness, 3-5-4; gravity, 3-7-8-8; color, blue; crystallization, 
monoclinic; cleavage, ——. 
Azurite is one of the rarest minerals of the district. The 
author has only seen a single specimen that has been posi- 
tively identified as this mineral. Linarite resembles it very 
much, especially in color, but is easily distinguished from 
it by chemical tests. 
Aurichaleite. 
Composition, 2(CuZn) COs 3(CuZn) (OH )2: Cu, 39-86%; Zn, 40-80%; O 
16-07%; C, 38-01%; H, 0-25 %. 
’ 
The crystallography of aurichalcite has never been com- 
pletely worked out. Even the crystal system to which it be- 
longs is in doubt. Belar“, who first described the crystals, 
refers it to the monoclinic system with B=90°, and gives its 
partial axial ratio a:b:c=1:x:0-7208. D’Achiardi” puts it 
in the monoclinic system with B=84° 15’; b:c=1:1-6574. 
Ceesars” concludes that the crystals described by him belong 
to the orthorhombic system with a tendency to pyramidal 
hemihedrism. 
The crystals studied by the author are monoclinic and the 
14. Belar: Zeit. of Kryst. u. Min. 17, pp. 118-122, 1889. 
15. D’Achiardi: Atti. delle Soe. Losec. gt Scienze Naturali Pisa, Memorie, 16, 1897, pp. 1-15; 
Abst. Nenes Jahr. f. Min., 1898, 1, p. 489, Ref 
16. Czesars: Mem. de L’ Academie Royal das Litt. et de B-A. de Belgique, 53, pp. 130-132, 1898. 
33—VIlil 
