DIAMOND
A scarce polymorph of carbon is diamond (C). The
physical properties of diamond and graphite couldn't be more different,
considering they have the same chemistry (they're both just carbon).
Diamond has a nonmetallic, adamantine luster, typically occurs in cubic or
octahedral (double-pyramid) crystals, or subspherical to irregularly-shaped
masses, and is extremely hard (H≡10). Diamonds can be almost any
color, but are typically clearish, grayish, or yellowish. Many diamonds
are noticeably fluorescent under black light (ultraviolet light), but
the color and intensity of fluorescence varies. Some diamonds are phosphorescent
- they glow for a short interval after a UV black light source is turned
off.
Diamond
(1.3 cm across) from Kasai-Oriental Province in central Zaire ("D.R.
Congo"). This 7.23 carat, dark-brown diamond mass is a complex
aggregate of several smaller diamond crystals. It comes from a late Late
Cretaceous (65-79 m.y.) kimberlite pipe in the Mbuji-Mayi Kimberlite Field.
Diamonds
from Africa - three yellowish-gray cubic diamonds & two clearish octahedral
diamonds. Crystal at lower left is ~2.5 mm across.
Diamonds
from Zaire (aka "D.R. Congo"). Each crystal is about 3
mm in size. These specimens don't significantly fluoresce under UV light.
Diamonds
from Zaire (aka "D.R. Congo"). Crystals are ~1 to 1.5 mm
in size.
Diamonds
from Zaire (aka "D.R. Congo") (same lot as above) fluorescing
under black light (UV). The green & magenta colors are from the
diamonds. The bright blue specks are fibers (not geologic
objects).
Diamonds
from Zaire (aka "D.R. Congo") (same lot & same view as
above) that are phosphorescent. No external light source is
present. The only source of light here is from the diamonds, just after
being subjected to UV light.
Diamonds
from Russia. Crystals are about 0.7 to 0.9 mm in size.
Diamonds
from Russia (same lot as above) fluorescing under black light (UV).
Diamonds
from an undisclosed locality fluorescing under black light (UV) (above
& below). Each crystal is on the order of 0.5 mm in size.
Diamonds
phosphorescing after removal of a black light source. Same lot & same
view as above.
Diamond
from Australia - brown octahedral crystal from the 1.178 billion year-old
Argyle Lamproite (Argyle Mine, nw Western Australia). The public has been
tricked into buying ugly brown diamonds by their being marketed as "cognac
diamonds". Light brown-colored
diamonds are cunningly marketed as “champagne diamonds”.
Faceted diamond (5.5 mm across). The image on the right shows
the famous "fire" of gem-quality diamond.
Left:
illuminated by four light sources.
Right:
illuminated by one light source.
Faceted diamond (~3.25 mm across).
Faceted diamonds in brooch (public display, Field Museum of Natural
History, Chicago, Illinois, USA).
See here for
pics of natural diamond crystals.