A crude Andalusite crystal that has
been cut with a diamond saw on one end. The end has been polished and set
on top of the crystal. This end cut shows the common cross like inclusions
that distinguish a variety of Andalusite known as Chiastolite.
This a
view of another Andalusite crystal (variety Chiastolite) that has been cut
perpendicular to the "C" axis.
This is a single crystal of
Andalusite from southern California.
CHEMISTRY - Al2SiO5
CRYSTALLOGRAPHY - Orthorhombic
CRYSTAL GROWTH AND HABITS - Andalusite typically forms columnar crystals with a nearly square cross section. It can also be fibrous, compact or massive.
COLOR AND OPTICAL PROPERTIES - Commonly a creamy white but can grade into brownish red or orange and sometimes greenish. It is transparent to translucent to nearly opaque with increasing amounts of inclusions. The variety Chiastolite has carbonaceous aligned inclusions as seen in the above photos.
HARDNESS - 6.5 - 7.5
SPECIFIC GRAVITY - 3.1 - 3.2
LUSTER - Vitreous
STREAK - White to light gray
BREAKABILITY - Andalusite has a good cleavage along {110} and poor cleavage along {100}. It has uneven to sub conchoidal fracture and is brittle.
OCCURRENCE - Andalusite is found in metamorphosed shales rich in aluminum. It is also found in granites and pegmatites. It can also be found as resistant grains in sedimentary rocks.
ASSOCIATED MINERALS - Kyanite, Sillimanite, Corundum, Cordierite, Garnet, Tourmaline, Mica and Quartz.
MINERAL NAME - Named after Andaluria, a province in Spain.