High quality Temolite tumblestones, each measuring approximately 18m by 20mm.
It belongs to a series with the minerals actinolite and ferro-actinolite. A series occurs when two or more ions can freely substitute between each other. In this case, when iron is predominant the mineral is ferro-actinolite and when magnesium is predominant the mineral is tremolite. Actinolite is the intermediate member and the most common followed by tremolite. Tremolite's formula is often written as the same as actinolite (with iron and magnesium), but specimens of tremolite can be found quite pure (that is, free of iron) and so here the formula reflects the pure end of the series. The entire series can be represented with the actinolite formula: Ca2(Mg, Fe)5Si8O22(OH)2.
Without the iron in the formula tremolite will have the typical creamy white color. With just a small amount of iron tremolite will be green. Increasing iron content will raise the specific gravity, index of refraction and darken the color.