Roeblingite

Character
Roeblingite is found in dense white compact masses made up of tiny prismatic crystals with parallel extinction and weak double refraction but too minute to enable the crystal system to be determined. The luster is rather dull, like that of unglazed porcelain; the hardness is just less than 3; and the specific gravity is 3.433.

Roeblingite is optically biaxial and positive; 2V small; elongation negative; a = 1.64, b = 1.64, g = 1.66. Under the iron-are spark it gives a very pale pink fluorescence or none at all.

Composition
As originally interpreted roeblingite is a lead-bearing calcium silicate containing a sulphite molecule. Later study by Blix (281a), however, has shown that no sulphite molecule is present but that all the sulphur is present as sulphate. The formula deduced by Blix is 2PbSO₄.Ca₇H₁₀Si₆O₂₄.

**Analyses of roeblingite**
	1	2	3	4
SiO₂	23.58	23.57	24.90	24.86
CaO	25.95	23.12	27.14	27.08
SrO	1.40	2.79
MnO	2.48	2.49
Na₂O	0.40
K₂O	0.13
H₂O	6.35	6.60	6.28	6.22
PbO	31.03	30.04	30.65	30.80
SO₂	9.00
SO₃		10.81	11.03	11.04
CO₂		0.61
	100.32	100.03	100.00	100.00

1. Average of two analyses. H. W. Foote (173), analyst.

2. Average of three analyses. R. Blix (281a), analyst.

3. Same as 2, after replacing SrO and MnO by their equivalent quantities of CaO, C02 by its equivalent quantity of silica, and recalculating to 100 percent.

4. Calculated for 2PbSO₄.Ca₇H₁₀Si₆O₂₄.

Occurrence
Roeblingite was described by Penfield and Foote (173), to whose data as given above little has been added. It was found, according to Mr. Nason, who sent the mineral to Penfield, at the 1,000-foot level of the Parker shaft near a contact of pegmatite and limestone, where a great abundance of garnet was developed. The largest mass found weighed about 5 pounds and was about the size and shape of a coconut. It, as well as other smaller masses found, was the center of a mass of cellular axinite, which in turn was contained in massive garnet. The many other associated minerals are of similar character to those accompanying the lead silicates nasonite and hancockite, found later in a similar pneumatolytic deposit, probably not far distant in the mine. But little of the mineral was preserved, and no other find was made until 1927, when a small amount was found, associated with calcium larsenite, clinohedrite, and other minerals characteristic of the Parker shaft mineral paragenesis.

Roeblingite was named in honor of the late Col. W. A. Roebling, of Trenton, N.J., the celebrated engineer, well known to mineralogists as an appreciative mineral collector.


	Website © by Herb Yeates 1997-2006.
	This page created: August 12, 2006 6:50 PM