Why does GIA certify amorphous carbon rock?

+3 GIA (Gemological Institute of America) often labels rocks like natural black diamonds (Carbonado) or sedimentary rocks containing large amounts of carbon as "amorphous carbon rock." Below are the specific details deciphering this term: Nature of the rock: This is a polycrystalline natural rock composed primarily of pure carbon, but these carbon particles are not arranged in a uniform crystalline structure. Composition: Although amorphous, this type of rock usually consists of a mixture of tiny, compressed diamond crystals interspersed with graphite and amorphous carbon. Commercial name: On the market, this type of rock is most commonly known as Carbonado (or cosmic black diamond). GIA calls them "rocks" rather than simply "gems" because of their unique structure, porosity, and origin. Origin: Numerous scientific studies suggest that this amorphous carbonaceous rock is highly likely to originate from outside Earth (meteorite explosions/meteorite impacts) or formed in deep underground environments. To learn more about the grading process for this particular material, you can refer directly to the Gemological Institute of America (GIA). Carbonado Diamond: A Review of Properties and Origin - GIA Aug 7, 2017 — CHARACTERISTICS OF CARBONADO. Carbonado is typically found in five major size categories: >200 ct, 75–95 ct, 25–35 ct, 8–15 ct, and 0.25–1.25 ct (see figure 5 o...