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biplane 
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Minerals recently investigated by M. Hermann. 409 
* above-mentioned authors had made it out a silicate of zinc. His 
Investigations transformed it into a silicate of manganese with 
the composition 
Si 30650 Mn46215 ¥e15-450 moisture and carbonic acid 7-300=99°615. 
Dr. Thomson’s reputation at that time served to put the blun- 
der on Vanuxem and Keating. The mineral was named Troos- 
tite, and Thomson’s analysis assumed as the correct one. 
cently the so-called Troostite has been examined by Hermann,* 
who has confirmed the original analyses, both results giving the 
formula Zn Si = Silica 72-47, oxyd of zinc 27-53, or the consti- 
tution of Willemite. The analyses hitherto made of the Ameri- 
can and foreign Willemite are as follows :— 
* 1, 2, Vanuxem and Keating (loc. cit.) ; 3, Hermann (loc. cit.) ; 
4, Thomson (Min. i, 545) ; 5, Levy (Ann. des Mines, [4], iv, 515); 
6, Rosengarten (Rammelsberg’s 3d Supplement to his Handwér- 
terbuch,°65) ; 7, 8, Monheim (Verh. Nat. Vereins. Rheinl., 1848, 
and Rammelsberg’s 4th Supplement, 114); 9, 10, Delesse (Ann. 
des Mines, [4], x, 211). 
2, “ 25:00. 7183 Be 0-67, Mn 26699: 
“« 26°80 60°07 Mn 9:22, Mg 2-91, Fe trace, loss by ignition 1:0=100 Herm. 
4,Moresnet,2697 68°77 Fe 1:48, 410-66, ib. & trace Zn, Pe 0°78, H 1:25=99'91, Thom. 
5, “ 27-05 68:40 #e 0-75, loss by ignition 0°30 = 96°50, Levy. 
6, Silesia, 27°34 70:82 Fe 1:81 99-97, Rosengarten. 
7, Stolberg, 26-90 72:91 Fe 0:35 = 100°16, Monheim. 
: 2653 69:06 * 436, Ca 0-41, Mg 0-13, 6 0:04 = 10053, Monheim. 
Si J 
1, Stirling, 25-44 68:06 ¥e, Mn 65010000, Vanuxem and Keating. 
66 “ “ 
9, “ 27-28 72:37 Fe 0°35 =100, Delesse. 
10, Stirling, 27-40 68°83 0:87, Mn 2°90 = 100, Delesse. 
Hermann gives the specific gravity of the Stirling ore 4-02; 
Vanuxem and Keating 389-4; Thomson for the Willemite 
3°935, and Levy 4:16-4:18. No. 7 (from Stolberg near Aix la 
Chapelle) was crystallized; G. = 4:18. o. 8 massive; G. = 
4:02-4:16. No. 10, the Stirling mineral, according to Delesse, 
has G. = 4°154. 
The crystals of Troostite have besides the primary rnombohe- 
dron (115°) another truncating its terminal edges, (-3 R) with 
R:R=142° 52’. The crystals of Willemite are quite small, be- 
ing but 2 or 3 millimeters long and 1 thick. They are hexa- 
gonal prisms, but the prism is intermediate to that of T'roostite ; 
and the trihedral summit has according -to Levy the angle of 
128° 30’ nearly, the planes not admitting of very accurate 
measurement,—corresponding possibly to the rhombohedron #R, 
which has this angle 127° 33’. 
— 
* Jour. fiir prakt. Chem. of Erdmann and Marchand, xlvii,"11. 
Szconp Series, Vol, [X, No. 27.—May, 1850. 52 
