CHAROITITE
The rare, impressively attractive, purple-colored
mineral charoite is only known from a relatively small area in
Siberia. Several odd, large igneous intrusions have been emplaced in
SiberiaÕs Baikal-Aldan Belt. One of these, the Murun Complex, consists of
several plutons. Emplacement of the Little Murun Pluton (Malyy Murun
Pluton) has resulted in significant contact metamorphism of surrounding
rocks. In the southern and southeastern contact aureole of the Little
Murun Pluton is a charoitite-carbonatite complex.
The charoitites are charoite-dominated contact
metamorphic rocks. Metasomatism refers to rocks that have been
altered by significant input of elements from an outside source. Because
thatÕs primarily what contact metamorphism is about, such rocks can be called metasomatites.
Some of the metasomatites in this area are purple-colored (ÒSirenevyy KamenÓ -
the ÒPurple StoneÓ deposit). The purple material is the very rare mineral
charoite. Charoite is a Ògarbage canÓ mineral, and the chemical
formula assigned to it by geologists varies from publication to
publication. Here's one of the formulas I've seen, randomly picked:
(K,Na)3(Ca,Sr,Ba,Mn)5Si12O30(OH·F)·3H2O
- hydrous potassium sodium calcium strontium barium manganese hydroxy-fluorosilicate.
Locality:
Charoitites are mined from several specific, relatively closely-spaced
localities in the headwaters areas of the Davan and Ditmara streams, south of
Olekminsk & the Lena River, way northeast of Lake Baikal, southwestern
Yakutia (Sakha), Siberia, Russia (~vicinity of 58¼ 22Õ North, 119¼ 11Õ East).
Age:
Aptian Stage, Early Cretaceous, 115-120 m.y.
Charoitite (charoite-dominated potassic metasomatite) (5.7 cm across) from the
Cretaceous of Siberia.