Description:
Wollastonite is a common mineral in skarns or contact
metamorphic rocks. Skarns can sometimes produce some
wonderfully rare and exotic minerals with very unusual
chemistries. However, wollastonite has no unusual elements
in its chemistry and it is somewhat common and not considered
very exotic among collectors. Wollastonite forms from
the interaction of limestones, that contain calcite,
CaCO3, with the silica, SiO2, in hot magmas. This happens
when hot magmas intrude into and/or around limestones
or from limestones chunks that are broken off into the
magma tubes under volcanoes and then blown out of them.
It forms by the following formula:
CaCO3 + SiO2 ----> CaSiO3 + CO2 Although not an "exotic"
mineral, wollastonite has its uses. It is an important
constituent in refractory ceramics (those ceramics that
are resistant to heat) such as refractory tile and as
a filler for paints. It is easily mined in some places
where it is the major component of the metamorphosed
rock. Mineral specimens can be interesting with their
fibrous habit, pearly luster and some specimens, especially
those from Franklin, New Jersey, will fluoresce. Wollastonite
is named for the English chemist and mineralogist W.
H. Wollaston (1766 - 1828). Its actual mineralogical
name is wollastonite - 1T. The 1T is for the Triclinic
symmetry of the most common and first described wollastonite
mineral. The reason the 1T is needed is to distinguish
it from the much more rare wollastonite - 2M, also known
as parawollastonite. Parawollastonite is Monoclinic.
These minerals are polymorphs which means that they
have the same chemistry, CaSiO3, just different structures
(poly means many and morph means shape). There are actually
several other rare and obscure polymorphs of CaSiO3
and are given the proposed names of wollastonite - 3T,
wollastonite - 4T, wollastonite - 5T and finally wollastonite
- 7T. All specimens named just wollastonite are most
likely wollastonite - 1T. |
