This is the light gray magnesite sphere. Diameter: 1.9″ (47mm). Weight – 5.7oz (161 grams). Origin: Russia, Siberia.
Some information about magnesite:
Magnesite is a mineral with the chemical formula MgCO3 (magnesium carbonate). Magnesite occurs as veins in and an alteration product of ultramafic rocks, serpentinite and other magnesium rich rock types in both contact and regional metamorphic terrains. These magnesites often are cryptocrystalline and contain silica in the form of opal or chert.
Magnesite is also present within the regolith above ultramafic rocks as a secondary carbonate within soil and subsoil, where it is deposited as a consequence of dissolution of magnesium-bearing minerals by carbon dioxide within groundwaters.