Actinolite

Actinolite is a silicate with composition Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂. The sample above is about 11x40 cm and is from Sears Creek, Wenatchee, National Forest, Washington. It has the form of pencil-like 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".