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Tremolite

Occurrence and Composition

Tremolite is found in marbles, often with talc or forsterite. It is an amhibole, and has end-member composition Ca₂Mg₅Si₈O₂₂(OH)₂. Some Fe may substitute for Mg, forming solid solutions toward actinolite.

Identification

Tremolite is identified by its bladed habit, amphibole cleavage, clear to pale green color and upper-first to low-second order interference colors.

Important Properties

·Appearance and habit - Tremolite typically forms blades, columnar or needle-like crystals.

·Color - Tremolite is clear to light green, may be slightly pleochroic. The color and pleochroism are more pronounced with greater Fe content.

·Cleavage - Tremolite shows typcial amphibole cleavage. One cleavage in longitudinal sections, and two creating a 60^o-120^o cleavage angle when viewed in end section.

·Interference colors - Maximum interference colors are upper-first to middle second order.

Similar Minerals

·Anthophyllite, another sometimes light or clear colored amphibole, has parallel extinction. Tremolite does not.

·Actinolite and hornblende have stronger coloration and usually a smaller 2V.

Tremolite in a Marble

This sample is a marble from the Adirondack Mountains, New York. Almost all of the field of view (about 2 mm across) is tremolite. The large grain in the center (viewed nearly down the c-axis) shows the classic amphibole cross section and cleavage. Smaller grains around it have their long axes in the plane of the thin section and so appear as long bladey crystals.

Talc in a Serpentenite (Verde Antique)

This is a talc-tremolite schist from the same location as the previous photos. The tremolite is clear in PP light and has 2nd order interference colors in the XP view. The talc, which has a dingy green color in the PP view, shows extremely high order interference colors -- almost "pearl white" in the XP view. The field of view of these photos is about 2.5 mm. This thin section was poorly made. Many small bubbles were trapped in the epoxy when it was prepared. They appear as small round circles in these pictures.