Actinolite is a relatively common mineral in some metamorphic
rocks. It belongs to a series with the minerals tremolite
and ferro-actinolite. A series occurs when 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.
A variety of actinolite is composed of microscopically
fibrous crystals (asbestos) and is called byssolite.
Other minerals also form asbestos such as serpentine
and the minerals of the series mentioned above. Serpentine
asbestos is more widely used and of a better grade in
general. Although asbestos has been shown to cause cancer
in humans when inhaled in high enough concentrations,
it still has many valuable applications. Asbestos is
used for fire retardant materials and brake shoes and
pads. Its prior use as insulation has been all but eliminated
due to health concerns. A variety of actinolite, nephrite,
is one of the two minerals called jade. The other jade
mineral is jadeite. Jade has been used for eons in China
and Central America as an ornamental and religious stone
of deep significance. The nephrite jade was used mostly
in China, although both have been used in both regions.
Nephrite is more abundant than jadeite and has few color
varieties, ranging only from creamy white to green.
Simple actinolite occasionally forms interesting crystal
habits and specimens. Crystals can be similar to hornblende,
but are always translucent or even transparent. Typically
they are prismatic, flattened and elongated. Crystal
specimens of actinolite can make very interesting mineral