830 The American Naturalist. [September, 

penetration twins, with the base the twinning plane. Harmotome is 
announced by Ferrier” as occurring in calcite filling vuggs in veins cut- 
ting the Animikie slates in the vicinity of Rabbit Mountain, Ontario. 
Besides calcite, the minerals associated with the harmotome are 
amethyst, fluorite; and pyrite. Black tin-bearing vw/z/e crystals, sup- 

posed to be from the Harney Peak district, in the Black Hills, have a. 
density of 5.294. Its composition, according to Headdn eand Pirsson, 
is TiO, = 90.79; FeO = 8.01; SnO, = 1.35. The habit is ortho- 
rhombic, with Poo, oPoo and P, twinned parallel to 11Poo. Tin 
ere has not yet been found in workable deposits in Texas. Most of the 
material from that state reported as being cassiterite is keilhanite,*4 
tourmaline, or black garnet.——Analyses of rhodochrosite from 
Franklin Furnace, N. J., yielded Browning,” after correcting 
impurities, the following figures : 
MVO CAG ZnO = MgO FeO FEO. CO Sp. Gr: 
OGG. TIAE TAG TJO 22 -10 40,40 3:47 

Miscellaneous.—It is a pleasure to know that Messrs. Clarke and 
Schneider” are busy with experiments looking toward the settlement 
of problems relating to the constitution of natural silicates. The 
methods employed by them resemble somewhat those that have afforded 
such excellent results in organic chemistry. Silicates are exposed to 
the action of hydrochloric acid gas at high temperatures, and to its 
solution at ordinary temperatures, and the effects in each case are 
noted. They are then ignited and subjected to other reagents, and 
the products here obtained are compared with the results of the former 
experiments. In this way the presence of groups of elements is recog- 
nized that are analogous to the residues of carbon chemistry. ‘Fhe 
conclusion already arrived at by the authors are to the effect of zade is 
an acid metasilicate (Mg,H,(SiO,),), and not a basic salt of pyrosilicic 
acid (Mg(Si,O,),(MgOH),) as Groth suggests. Serpentine is thought 
‘be a substituted orthosilicate corresponding to Mg,(SiO,),H,(MgOH), 
and its relation to olivine and chondrodite are represented as follows : 
Olivine = Mg,(SiO,),; chondrodite = Mg,(MgF)(SiO,), ;_ serpen- 
tine = Mg,(MgOH)H,(SiO,),. Ch/orite is regarded as R”,(SiO,),R’, 
or olivine with half the magnesiem replaced by R’, and the fluoriferous 
- Tb., Feb., 1891, p. 161. 
> 
26 Ib., 1890, XL., p. 312, 405. 

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