Actinolite is a silicate with composition Ca2(Mg,Fe)5Si8O22(OH)2, all big-8 elements except hydrogen. The sample above is about 11x40 cm and is from Sears Creek, Wenatchee, National Forest, Washington. It tends to form in long, thin crystals. These samples are displayed in the Smithsonian Museum of Natural History.

This actinolite sample shows a formation pattern somewhat similar to the above, but very different from the fibrous form below. This sample is formed after pyroxene. It is about 20x16 cm and is from Calumet mine, Salida, Colorado.

This sample of actinolite has a very different appearance, forming in a fibrous mass. The sample is about 18x16 cm and is from Fairfax quarry, Centreville, Virginia. It has an appearance similar to those magnesium silicates which are collectively labeled "asbestos".

This sample is labeled as an actinolite-talc schist. It is evaluated to be a Catalina Schist of about 100 million years age from the Santa Catalina Island, California. The container of water shows how much water the rock contains. It formed deep in a subduction zone when the altered oceanic lithosphere began to release water. The sample is about 25 x 20 cm.

These large crystals of quartz have actinolite inclusions.

Mindat: Actinolite

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