Geological Properties Of Tremolite

Geological Properties Of Tremolite. Tremolite is an important rock-forming mineral and occurs most commonly as a white to light green, granular to fibrous component of metamorphosed carbonate rocks, especially skarns and dolomite marbles, where the crystals and aggregates can become quite large. Any light colored amphibole in a marble will normally be tremolite. Large isolated and well-terminated crystals are rare. In this environment, it commonly forms as pseudomorphs of tremolite after diopside, but can also be primary. Tremolite is also common in many metamorphosed mafic and ultramafic rocks such as amphibolites and metabasalts although actinolite and other iron-rich amphiboles usually dominate there. Fibrous (asbestiform) tremolite veins are common in many metamorphic rock types, especially where they are carbonate-bearing. In meta-igneous rocks, cummingtonite and anthophyllite can be difficult to distinguish from tremolite, but these are more restricted to metamorphosed Ca-poor ultramafic rocks like serpentinites.

Tremolite is a silicate mineral and member of the amphibole group. Chemical formula is Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2. A calcium magnesium silicate, tremolite forms a solid-solution series with ferroactinolite, where iron substitutes in increasing amounts for magnesium. The color of tremolite varies with increasing iron content from colorless to white in pure tremolite to gray, gray-green, green, dark green and nearly black in other specimens. Traces of manganese may tint tremolite pink or violet. When well-formed, crystals are short to long prisms. More commonly, tremolite forms unterminated bladed crystals, parallel aggregates of bladed crystals, or radiating groups. Tremolite and actinolite both form thin, parallel, flexible fibers up to 10 in (25 cm) in length, which are used commercially as asbestos. Tremolite is known as nephrite jade when it is massive and fine-grained. The mineral is abundant and widespread. It is the product of both thermal and regional metamorphism and is an indicator of metamorphic grade because it converts to diopside at high temperatures (1,065°F/575°C or above).

Tremolite occurs as a result of contact metamorphism of calcium and magnesium rich siliceous sedimentary rocks and in greenschist facies metamorphic rocks derived from ultramafic or magnesium carbonate bearing rocks.

Geological Properties Of Tremolite

Associated minerals: include calcite, dolomite, grossular, wollastonite, talc, diopside, forsterite, cummingtonite, riebeckite and winchite.

Crystallography: Monoclinic; prismatic. Crystals prismatic in habit; the prism faces make angles of 56° and 124° with each other. The termination of the crystals is almost always formed by the two faces of a low clinodome (Figs. 400 and 401). Tremolite is often bladed and frequently in radiating columnar aggregates. In some cases in silky fibers. Coarse to fine granular. Compact

Tremolite Composition: Ca2Mg5Si80 22 (0 H )2, is an end member of an isomorphous series. Iron may replace magnesium in part, and when present in amounts greater than 2 per cent, the mineral is called actinolite

Tremolite Diagnostic Features: Characterized by slender prisms and good prismatic cleavage. Distinguished from pyroxenes by the cleavage angle and from hornblende by lighter color.

Countries of Origin

Tanzania, United Republic Of; Afghanistan; United States of America; Switzerland; Canada; Austria; Unknown; Norway; China; Italy; Australia; France; Germany

Occurrence of Tremolite

Tremolite is most frequently found in impure, crystalline, dolomitic limestones where it has formed on the recrystallization of the rock during metamorphism. It is also found in talc schists. Actinolite commonly occurs in the crystalline schists, being often the chief constituent of green-colored schists and greenstones. Frequently the actinolite of such rocks has had its origin in the pyroxene contained in the igneous rock from which the metamorphic type has been derived.

Geological Properties Of Tremolite

Tremolite Uses Area

The fibrous variety is used to some extent as asbestos material. The fibrous variety of serpentine furnishes more and usually a better grade of asbestos. The compact variety nephrite is used largely for ornamental material by oriental peoples.

Tremolite Physical Properties

Crystal habit: Elongated prismatic, or flattened crystals; also as fibrous, granular or columnar aggregates
Color White, brown, colourless, grey, light green, green, light yellow, pink-violet
Streak: White
Luster: Vitreous, Silky
Cleavage: Perfect on {110}
Diaphaneity Transparent, Translucent
Mohs Hardness: 5 – 6
Crystal System: Monoclinic
Tenacity: Brittle
Density 2.99 – 3.03 g/cm3 (Measured) 2.964 g/cm3 (Calculated)
Fracture: Splintery
Parting on: {010} {100}
Tremolite Optical Properties
2V: Measured: 88° to 80°, Calculated: 82° to 84°
R:I values: nα = 1.599 – 1.612 nβ = 1.613 – 1.626 nγ = 1.625 – 1.637
Twinning Simple or multiple: common parallel to {100}, rarely parallel to {001}
Optic Sign Biaxial (-)
Birefringence δ = 0.026
Relief Moderate
Dispersion: r < v weak