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(Ca,Na)2Mg5Si8O22(OH)2
Monoclinic, C2/m, a = 9.846, b = 18.092, c
= 5.297 Ć,
b = 104.50o, Z = 2
Tremolite is a common mineral in the Franklin Marble, occurring with other silicates in aggregates and as isolated crystals. Tremolite has been little studied locally. Nuttall (1822) noted it originally and Palache (1935) provided some data; otherwise the extant study is that of Klein and Ito (1968), from which these data were taken.
Tremolite occurs as euhedral crystals in much of the Franklin Marble; some are rounded, and some are up to 10 cm in length. Tremolite is colorless to white or gray, with vitreous luster, normal amphibole prismatic cleavages, and a density of approximately 3.1 g/cm3. Optically, it is biaxial, negative, with a = 1.614, b = 1.629, and g = 1.640; pleochroism is absent. In ultraviolet, much tremolite from the Franklin Marble fluoresces light blue in shortwave; some specimens fluoresce light yellow in longwave. Dorling and Zussman (1984) found a zincian tremolite with asbestiform habit to have abundant Wadsley defects on {010} and multiple twinning on {100}; they also observed fibrils with a triple-chain structure.
Tremolite is a calcium magnesium silicate hydroxide mineral of the amphibole group. A representative analysis is given in Table 12. Other unpublished analyses by the writer indicate that tremolite can contain up to 5 wt.% MnO and 6 wt.% ZnO, in material with 2 wt. % FeO. There exists in local specimens a complete solid solution series from end-member tremolite, through actinolite, to ferroactinolite containing barely 52 mole % of the end-member.
Tremolite is found as euhedral crystals and mixed with other accessory minerals in much of the Franklin Marble. It has been found in many of the local quarries and rarely in the calcium silicate units of the orebody; actinolite is more common in the Franklin orebody, especially in proximity to the franklinite ores. The tremolite studied by Klein and Ito (1968; #4) was associated with rhodochrosite and calcite in a vein in franklinite-calcite ore in which the tremolite is separated from the ore by carbonates. Frondel (1972) has reported tremolite as one of the white fibrous amphiboles found, alone and sometimes mixed with zincite, on slickensides; this intimate mixture with zincite is known locally as calcozincite (Shepard, 1876). Much serpentine also may be found in this material, together with other fibrous minerals.
In the marble, fine crystals, 10 cm and more in length, have been found associated with graphite, chondrodite, calcite, arsenopyrite, phlogopite, chlorite, and a large number of other species. Such tremolite crystals are occasionally warped and fractured, and some broken ones are “healed” by other minerals. They may contain inclusions of other minerals. Amphiboles in the marble were studied by Germine (1986).
At Sterling Hill, tremolite was found in an asbestiform habit on slickensides in the 1680 stope, just below the 1400 level.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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