Hydrohetaerolite

Habit
Hydrohetaerolite is found in fibers grouped in radiated masses with botryoidal or mammillary surfaces, also in massive granular and bladed forms. The appearance of a typical specimen is well shown in plate 19, A.

Physical characters
In mass the mineral is dark brown to black, with submetallic luster, and not unlike fibrous limonite in appearance. Under the microscope the fibers are dark brown, weakly pleochroic, and doubly refracting, with extinction parallel to their length. Cross sections of them show an obscure square form indicating a poor prismatic cleavage, and they give a faint uniaxial figure in convergent polarized light, indicating probable tetragonal crystallization. The mineral is uniaxial and negative, with faint pleochroism in red-brown colors. In absorption e > w; w = 2.34 ±0.02 and e = 2.14 ±0.02 (Larsen). The streak is dark brown, the hardness is 5, and the specific gravity is 4.93 (Moore) or 4.85 (Schaller).

Composition
An analysis of type material from Sterling Hill, supplied by Mr. Hancock, shows the mineral to be a hydrous oxide of manganese and zinc. The ratio indicates a close approximation in composition to the accepted formula.

**Analysis of hydrohetaerolite**
	1	2	3
Mn₂O₃	60.44	61.34	0.393 = 1.88†
Fe₂O₃	0.77	0.78
ZnO	33.43	33.93	0.416 = 2.00
H₂O-	2.47	3.95*	0.220 = 1.05
H₂O+	1.42
SiO₂	1.71
	100.24	100.00

[* figure represents combined H₂O- and H₂O+]

[† figure represents Mn₂O₃ + Fe₂O₃]

1. Type material from Sterling Hill. W. T. Schaller (Palache, 195), analyst.

2. Same analysis recomputed to 100 percent after omission of SiO₂.

3. Molecular ratio, computed from the analysis.

Occurrence
Hydrohetaerolite is invariably associated with crusts of chalcophanite. This association was believed by Moore to be due to a progressive alteration of franklinite through hydrohetaerolite to chalcophanite, a theory for which there is strong confirmation in the observed facts of occurrence. (See first column on this page.)

Hydrohetaerolite was found only at the Passaic mine, Sterling Hill, where it was abundant and was first recognized as a distinct mineral by Moore (114). As he gave no analysis and his description was incomplete, his conclusion that it is a zinc hausmannite was not accepted. For the further history of this mineral see under hetaerolite on page 49.


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	This page created: January 12, 2001 6:26 PM