Desaulesite

Character
Desaulesite forms crusts and formless aggregates filling cavities in purple fluorite and replacing rough crystals of niccolite. The aggregates are built up loosely in gratelike or spongelike porous forms, the linear, intersecting, cylindroid rods being covered with faceted knobs like crystalloid bodies. It is found also in massive compact layers and in earthy form. Its color is yellowish green to bright apple-green and emerald-green. Its refractive index is 1.59.

Desaulesite was named by Koenig in honor of Maj. A. B. de Saules, former manager of the Trotter mine. As described by Koenig (137), it was found in some abundance in intimate association with chloanthite at the Trotter mine. The specimens in the Hancock collection show it associated with niccolite and chloanthite in such a way as to leave no doubt that it is an alteration product of those minerals.

Composition
Desaulesite is a hydrous nickel silicate related to genthite but containing little or no magnesium.

**Analyses of desaulesite**
	1	2	3	4
SiO₂	31.62	27.33	30.89	0.512	= 3 x 0.171
NiO	38.22	43.78	46.08	0.616*	0.661 = 4 x 0.165
ZnO	4.00	1.92	2.17	0.025*
FeO	2.03	1.19	1.34	0.018*
MnO		0.11	0.13	0.002*
CaO	0.71	Trace
MgO	0.42	Trace
As₂O₅	4.77
As₂O₃		7.99
H₂O +	7.14	10.59	19.39†		1.077 = 6 x 0.180†
H₂O -	9.44	6.57
	98.35	99.48	100.00

[* Figures reflected in value 0.661 shown.]

[† Combined water.]

1. Original material, 0.28 gram. G. A. Koenig (137), analyst.

2. Abundant material. L. H. Bauer (243), analyst.

3. Analysis 2 recomputed to 100 percent after deducting 8.42 percent of NiAs₂, equivalent to the As₂O₅ found.

4. Molecular ratio computed from no. 3.

The analysis by Koenig is unsatisfactory. He explained the arsenic as present in annabergite, nickel arsenate, 12 percent of which would have to be deducted. The residue could then be computed approximately to the formula of garnierite. Optical examination of typical material failed to reveal any trace of annabergite but showed minute metallic specks that might well be one of the arsenides. In the new analysis the arsenic was determined by Bauer to be the trioxide, which could be better explained if present in a nickel arsenide, such as chloanthite, and the analysis was so interpreted.

The molecular ratio obtained leads to a formula of the same type as that assigned to genthite, except that magnesium is lacking. Desaulesite may therefore be grouped with deweylite and genthite its shown below:

Deweylite	4MgO.3SiO₂.6H₂O
Genthite	2NiO.2MgO.3SiO₂.6H₂O
Desaulesite	4NiO.3SiO₂.6H₂O


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