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
Siberia’s 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
that’s primarily what contact metamorphism is about, such rocks can be
called metasomatites. Some of the metasomatites in this area are
purple-colored (“Sirenevyy Kamen” - the “Purple Stone”
deposit). The purple material is the very rare mineral charoite.
Charoite is a “garbage can” 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 58º 22’ North,
119º 11’ East).
Age:
Aptian Stage, Early Cretaceous, 115-120 m.y.
Charoitite (charoite-dominated potassic metasomatite) (5.7 cm across) from the
Cretaceous of Siberia.