- "Black lead." A mineral composed entirely of carbon. Very soft because
of crystalline structure;
diamond, in contrast, has same composition but its
hardest substance known.
Source: Leet, L. Don. 1982.
Physical Geology, 6th Edition. Englewood Cliffs, NJ: Prentice-Hall
- A hexagonal and trigonal mineral, native carbon 4[C] , polymorphous with
chaoite, diamond, and lonsdaleite; scaly, soft, lustrous, metallic; greasy
feel; as crystals, flakes, scales, laminae, or grains in veins or bedded
masses or disseminations in carbonaceous metamorphic rocks; conducts
electricity well, is soft and unctuous; immune to most acids; extremely
refractory. Syn: plumbago; black lead.
Dictionary of Mining, Mineral, and Related Terms