A
prismatic mass of Actinolite
crystals displaying their typical greenish color.
A close-up view
of the above picture.
This is a
fibrous mass of Actinolite. It is also called Byssolite. This
specimen is part of the Arizona Mining and Mineral Museum Collection, #
MM-T350
CHEMISTRY Ca2(Mg,Fe)5Si8O22(OH)2 Calcium, Magnesium-Iron Silicate
CRYSTALLOGRAPHY Monoclinic
CRYSTAL GROWTH AND HABITS Crystals are often bladed or columnar, actinolite is also found as radiating fibers or acicular crystals and massive to granular.
COLOR AND OTHER OPTICAL PROPERTIES Green to grayish green and transparent to translucent.
HARDNESS 5 - 6
SPECIFIC GRAVITY 3.0 - 3.2
LUSTER Vitreous
STREAK White
BREAKABILITY Actinolite has good prismatic cleavage at angles of 56o and 124o. It is brittle, but tough when it forms fibrous masses (as in nephrite jade).
OCCURRENCE Actinolite forms through the processes of low grade regional metamorphism of dolomitic sediments or ultramafic igneous rocks.
ASSOCIATED MINERALS Talc, Epidote, Chlorite