Mcgovernite

Physical character
Crystals of mcgovernite are not known. It is found in coarse granular form, the individual grains showing pronounced micaceous cleavage. In reflected light it is bronzy red, and in transmitted light it is deep red-brown. It is optically uniaxial and positive; w = 1.754. The cleavage is basal, very perfect, like that of friedelite, and the mineral is therefore presumably hexagonal. Its specific gravity is 3.719.

Composition
Mcgovernite is a complex basic manganese, magnesium, and zinc arseniosilicate.

**Analysis of mcgovernite**
(L. H. Bauer (252), analyst)
	Percent	Molecular ratio
SiO₂	8.92	0.48	= 3 x 0.049
MnO	42.73	0.603*
FeO	1.53	0.021*	1.029 = 21 x 0.049
MgO	11.27	0.280*
ZnO	10.22	0.125*
As₂O₃	4.45	0.023	= 0.5 x 0.046
As₂O₅	12.48	0.054	= 1 x 0.054
H₂O	8.49	0.472	= 10 x 0.047
	100.08

[* Figures reflected in the 1.029 value shown.]

The presence of arsenic in two states of oxidation, which is unique among minerals, was carefully established by the analyst and must be accepted as a fact in attempting to interpret the analysis. No simple formula can be derived from the stated composition, and until the results of more analyses are available and the true nature and relations of the mineral are better known it is not feasible to derive a formula showing the chemical structure. The following provisional formula was suggested in the paper by Palache and Bauer (252): 21(Mn,Mg,Zn)O.3SiO₂. (As₂O₃)_0.5.As₂O₅.10H₂O. The possible relation of the mineral to dixenite and the minerals of the friedelite group is treated in the paper by Bauer and Berman (260).

Occurrence
Mcgovernite was found in 1927 in the mine at Sterling Hill, in the north drift, 900-foot level. It forms the principal filling of a vein in massive ore, as a rather uniformly coarse-grained mass. But few specimens of it have been preserved.

The mineral is named for J. J. McGovern, of Franklin, who died in 1915. For many years he was in charge of the picking table at the shaft head, and he was one of the foremost of the local collectors and added much to the knowledge of Franklin mineralogy.


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