Hastingsite (Gamsigradite) |
Black hornblende, both granular and in large and complex crystals, was found in abundance at Sterling Hill in immediate association with the ore body. It was recorded first by Credner (90) as a constituent of the pegmatite there but was doubtless often mistaken for jeffersonite, with which it is associated. The crystals, which are black but not uncommonly have a dull-gray coating, are generally prismatic parallel to the clinoaxis and reach dimensions that are very large for the species. The largest one seen, in the collection of T. Lang, is 18 inches long parallel to the clinoaxis and 6 inches across in the directions parallel to the other two axes. A similar one is shown in plate 10, B, and figure 102.
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Figure 102 Crystal of hastingsite showing the forms b(010), m(110), p(101), r(011), i(031), k(211), v(231) and z(121). Sterling Hill. A, Plan; B, clinographic projection. |
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Similar material, found with franklinite and sold as jeffersonite, was described by Kloos (121) from Franklin. Local collectors could give no information of such material from Franklin, but as Kemp also mentions finding such crystals there it seems probable that the mineral has been found at both localities. The following data were taken from the full description of this hornblende by Kloos: The crystals are unsymmetrical, are prismatic parallel to the vertical axis, are flattened parallel to the clinopinacoid, and are a fifth of an inch to an inch long parallel to the vertical axis.
The edges are rounded, the faces and cleavage surfaces are lustrous, and the color is deep leek-green where not coated with manganese oxide. Very thin sections are translucent green; the axial colors are, parallel to X, honey-yellow; to Y, yellowish green; to Z, bluish green. The extinction angle to the vertical axis is 17° 15'. The specific gravity is 3.352. The powder is soluble in hydrochloric acid.
| SiO2 | 39.59 |
| TiO2 | 1.76 |
| Al2O3 | 11.20 |
| Cr2O3 | 0.13 |
| Fe2O3 | 5.97 |
| FeO | 11.31 |
| MnO | 3.07 |
| ZnO | 0.53 |
| MgO | 8.42 |
| CaO | 12.85 |
| N2O | 3.31 |
| K2O | 1.95 |
| H2O | 1.02 |
101.11 |
This amphibole was called by Dana "gamsigradite", a name first applied in 1861 by Breithaupt to a closely similar manganiferous hornblende from Gamsigrad, in Serbia. It differs from hastingsite only in containing a little manganese.
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© by Herb Yeates 1997-2006.
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page created: August 12, 2006 8:11 PM
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