49 
and results apply to experiments, etc., carried out, except when 
otherwise stated, on the mineral from that locality. 
The Kanowna al unite is a white, firm, finely crystalline mass, 
resembling 1 somewhat in appearance a compact clay, for which it 
might readily be mistaken. It breaks, when freshly mined, with a 
typical snap similar to the breaking of a biscuit. After exposure 
to air for a few days in a comparatively dry atmosphere many 
specimens of the mineral disintegrate into a fine powder, due to the 
presence of admixed salts. If allowed to partly dry and then again 
wetted, it shows a tendency to soften and crumble; this is probably 
due to partial dehydration and then absorption of water by thc$ 
colloids clay, etc.) present. The mineral is extremely porous 
and tests carried out on several pieces dried at 80° C. gave 22.0 
18.1 and 10,8 per cent, of water absorbed by weight, the air space 
by volume being 58.2, 48.0 per cent,, and 28.6 per cent., respectively. 
The powder, under the microscope, appears as minute, colour- 
less, transparent, cubical grains, which have been determined by 
Dr. Simpson as “not true cubes of the isometric system, but rhom- 
bohedrons approximating to cubes.” This is shown by their optical 
properties, the crystals being anisotropic with diagonal extinction. 
The individual crystals are very minute, ranging in size from 3 to, 
at the most, 10 microns. The specific gravity was determined in 
methylene iodide and proved to be very close to that of quartz, viz., 
2.05. The refractive index was determined by mounting some of the 
powder on slides with liquids of known refractive index and ex- 
amining them under a microscope. The mineral agreed with that 
of oil of cassia, having a refractive index of 1.58. 
The refractive index affords a simple and ready method for the 
detection of alunite by immersion. The mean refractive indices of 
minerals resembling alunite in appearance are — 
Kaolin 
. . 
. . 1.54 
Quartz 
* • 
. . 
. . 1.547 
S eri cite 
. . 
, , 
. . 1.587 
Cal cite 
0 • 
, . 
.. 1.601 
Magnesite . . 
♦ • 
, , 
.. 1.72 
The alunite from Kanowna is invariably associated with appreciable 
amounts of water soluble salts and a little quartz, kaolin and mica, 
The empirical formula for alunite is — 
K 2 0, 3A1A-4S0 ; ,GIL0. 
which may he represented as K 2 SO j .A1 ;j (SO i1 ) r . 4A1(OH) 3 . but for 
reasons which will be dealt with later, would be more correctly 
written as JvS O ,.3HO A 1 S ( ) 4 .3 Al ( OTI ) ... 
