What is diamond? (3.01)
Simply put, diamond is pure carbon that has crystallized in the isometric (cubic) configuration. It is the only single-element gem that exists on this planet. (Carbon -- expressed as C in the periodic table.) Elemental carbon occurs only in three natural forms: diamond, graphite, and amorphous carbon. Amorphous carbon occurs as a type of soot produced by partly-burned hydrocarbons, such as kerosene and natural gas.
Courtesy of: Upper Left: Rudn University: https://e3.eurekalert.org/news-releases/725859
Upper Right: By Rob Lavinsky, iRocks.com – CC-BY-SA-3.0, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=10164225
Lower Left: White Flash: https://www.whiteflash.com/blog/guide-to-rough-diamonds/