Second occurrence of okayamalite, Ca2SiB2O7: chemical and TEM characterization

Okayamalite, Ca2SiB2O7, was identified in a skarn sample from the Arendal d istrict, Sorlandet, Norway, associated with datolite, calcite, apophyllite, and chlorite. The chemical composition was determined by analyzing both he avy (Ca and Si) and light (B and O) elements using an electron microprobe: the empirical formula based on seven O atoms is Ca1.96Si0.97B2.07O7.00. TEM investigation revealed that okayamalite is intergrown on a fine scale with amorphous silica, giving rise to a complex interpenetrating structure at t he scale of few hundreds angstroms. Okayamalite probably was formed by a de silication-dehydroxylation process of the associated datolite.