Kaminsky et al. (2019) described enigmatic polycrystalline diamond from the placers on Aynyn River at Kamchatka peninsula and named them “kamchatite.” The samples were picked up from the mineral separates in the alluvial deposits. They are up to 1 mm in size and have a rounded shape. Octahedral and irregular diamond crystallites (2–40 μm in size) occupy about 50 vol% of the aggregates. The matrix cementing the diamond crystals consists of Ca5(Si2O7)(CO3)2 tilleyite, SiC, Fe-Ni-Mn-Cr silicides, native silicon, graphite, calcite, and some amorphous material. Three types of composition of the amorphous...

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