392 
When heated, in a solution of Cobalt, it turns blue, and 
gives distinct reactions with Fluor. After roasting, the fact 
of Hydrofluoric, or Muriatic acids, having no effect is a 
distinguishing feature. 
Dr. Sommerlad’s analysis gave the following results :— 
Silicious Acid se ine ui AS 33°34 
Aluminous Acid ... ie ae am 37°02 
Lime a Mee aa a vie 0°83 
Fluor By ME i ae us 17°64 
Mota lasses Bae OPE 
Specific Gravity... 3°456 
The alterations from the normal composition of Topaz 
(5 Al Si O05 + Al Si F110) are very insignificant, indeed, and 
they may be attributed to these impurities, the existence of 
which haye been demonstrated when under the microscope, 
but the percentage of Lime is very remarkable as such cannot 
belong to the Topaz proper, but is due to other minerals 
interspersed through the rock. The “slides” of this dense 
white Topaz exhibit an aggregate of irregularly deposited 
streaky or oblong groups of needle-like prisms from 0-01 to 
0°05 min. in width, to 0:04 to 0°3 min. in length, showing also, 
across their diameter vivid rainbow-like colours, which, how- 
ever, disappear entirely with their longer axis. Only very 
rarely—as quite natural—are the rhombic cross-sections 
observable in the directions just alluded to. The terminal 
apices of these prisms resemble those, with crystallized Topaz, 
customary pyramidal and domatic points.* 
To judge from the specimens now before me, dense Topaz, 
intermixed with dense greyish blue Tourmaline, can easily be 
discerned with the naked eye, though the latter occurs in 
forms unlike its usual character, maintaining, however, the 
ordinary fibrous forms. 
Tourmaline is seen distinctly in the “ slides,” in the form 
of botryoidal nests and as filling cavities of the Topaz rock. 
3. ToURMALINE FROM M7. BiscHorFrr. 
This occurs also in the Carbonates of Iron as needles 
measuring 0°25 mm. thick, to 1 m. in length, from dark 
green to blackish colours. “Slides” exhibit the same like- 
wise, as a dirty violet nucleus, which is enveloped by a 
sreenish coating. Their pleochroism is very strongly marked, 
and the colouring partakes of lighter and stronger tints, 
according to the manner and position in which the crystals 
# G. vom Rath has already described Topaz crystals from the Waratah 
Mine, Mount Bischoff, as from 4 to 4 min. in size. These crystals formed 
fine crystalline aggregations in which crystals of Cassiterite were embedded. 
Also the occurrence of nests of radiating crystals of Pycnite. Bonn, 1879. 
