Magnesium chlorophoenicite

Habit
Magnesium chlorophoenicite is found in fibers, grouped in radial aggregates implanted on the surface of a narrow open vein composed of zincite and carbonates. Some of the rosettes have a diameter of two-fifths of an inch.

The only specimen known was collected by the late George Stanton in the Franklin mine on the 750-foot level at pillar 859.

Physical properties
The fibers are white or colorless but are stained brown on some surfaces. They show the same single excellent cleavage lengthwise of the fibers that is characteristic of chlorophoenicite. The specific gravity is 3.37.

Optical properties
The mineral is optically biaxial and positive, with a small optic angle. The plane of the optic axes is across the fibers—that is, parallel to the plane of crystal symmetry. The extinction angle could not be measured on the material available; r < v (strong); a = 1.669, b = 1.672, g = 1.677, all ±0.003 (Berman).

Composition
Magnesium chlorophoenicite is similar in composition to chlorophoenicite but contains magnesium in place of all the zinc and part of the manganese of that mineral. The following analysis was made in the chemical laboratory of the department of mineralogy at Harvard University on about 0.4 gram of material that could not be completely purified without loss of too much of the mineral itself.

**Analysis of magnesium chlorophoenicite**
	1	2	3	4	5
SiO₂	3.36	0.056
Fe₂O₃	3.85	0.024
ZnO	8.90	0.109
MgO	29.95	0.743	0.743* = 10 x 0.093	39.64	39.31
MnO	15.57	0.219	0.188*	18.05	17.29
As₂O₅	21.16	0.092	0.092 = 1 x 0.092	28.00	28.04
H₂O	10.81	0.601	0.601 = 7 x 0.086	14.31	15.36
CaCO₃	6.29	0.063
	99.89			100.00	100.00

[* These two figures combined reflect the value 10 x 0.093.]

1. Magnesium chlorophoenicite, Franklin. F. A. Gonyer (277), analyst.

2. Molecular equivalents of the constituents.

3. Molecular ratio of remainder after deducting 5.55 percent of franklinite, 6.29 percent of calcite, and 12.49 percent of Willemite.

4. Composition of remainder recomputed to 100 percent.

5. Composition of mineral computed from formula, assuming the molecular ratio of MnO to MgO as 1 to 4.

The material analyzed was known to contain calcite and willemite, and in interpreting the analysis the assumption was made that all the ZnO and SiO₂ found was contained in willemite and that all the Fe₂O₃ found was contained in franklinite. On this assumption the material contained 24.32 percent of impurities, consisting of 6.29 percent of calcite, 12.48 percent of willemite, and 5.55 percent of franklinite. The molecular ratio of the remainder gives the empirical formula 10(Mg,Mn)O.As₂O₅.7H₂O, which is of the same form as that of chlorophoenicite but differs in containing magnesium in place of zinc, the molecular ratio of MgO to MnO being 4 to 1.

The difference in composition is reflected in the lower specific gravity, lower refractive indices, and opposite optical sign of the mineral as compared with chlorophoenicite. This may explain the fact previously discovered that some specimens of what was taken to be chlorophoenicite are optically positive.


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	This page created: January 12, 2001 6:31 PM