Mineral allotrope of carbon. It is dark gray to black, opaque, and very soft. Its layered structure, with rings of six atoms arranged in widely spaced parallel sheets, gives it its slippery quality. It occurs in nature and is used (mixed with clay) as the “lead” in pencils. It is also used in lubricants, crucibles, polishes, arc lamps, batteries, brushes for electric motors, and nuclear reactor cores.
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Plumbago is a genus of 10-20 species of flowering plants in the family Plumbaginaceae, native to warm temperate to tropical regions of the world. Common names include plumbago and leadwort (names which are also shared by the genus Ceratostigma). The name Plumbago is derived from Latin plumbum ("lead"), either from the lead-blue flower colour of some species (OED), or from the plant at one time being a supposed cure for lead poisoning (Huxley 1992).
The species include herbaceous plants and shrubs growing to 0.5-2 m tall. The leaves are spirally arranged, simple, entire, 0.5-12 cm long, with a tapered base and often with a hairy margin. The flowers are white, blue, purple, red, or pink, with a tubular corolla with five petal-like lobes; they are produced in racemes.
The flower calyx has glandular hairs, which secrete a sticky mucilage that is capable of trapping and killing insects; it is unclear what the purpose of these hairs is; protection from pollination by way of "crawlers" (ants and other insects that typically do not transfer pollen between individual plants), or possible subcarnivory (Schlauer 1997).Selected species