A crystalline form of → carbon, which is the hardest substance known. Each carbon in a diamond crystal is bonded to four other carbon atoms forming a tetrahedral unit. This tetrahedral bonding of five carbon atoms forms an incredibly strong molecule. Diamond has a very high → refractive index and → dispersive power. It is colorless when pure, and sometimes colored by traces of impurities. Natural diamond was formed billions of years ago within the Earth → mantle at depths greater than 150 km, where pressure is roughly 5 giga→ pascals and the temperature is around 1200 °C. Diamonds reach the surface of the Earth via volcanic eruptions. Similarly very small diamonds (micrometer and nanometer sizes) are usually found in impact sites of → meteorites. Such impact events create shock zones of high pressure and temperature suitable for diamond formation. When diamond is exposed to high temperatures or ion bombardment, it will be transformed into → graphite.
Diamond, from O.Fr. diamant, from M.L. diamant-, diamas-, from L. adamant-, adamas "hardest metal," from Gk. adamas "unbreakable," from → a- "not" + daman "to subdue, to tame;" cognate with Pers. dâm "a tame animal."
Almâs, loanword from Gk., as above.
diamond ring effect
oskar-e angoštar-e almâs
Fr.: effet anneau de diamant
An intense flash of light that happens a few seconds before and after totality during a solar eclipse. The effect is caused by the last rays of sunlight before totality (or the first rays of sunlight after totality) shining through valleys on the edge of the Moon.
Oskar, → effect; angoštar "a ring worn on the finger," from angošt "finger," Mid.Pers. angušt "finger, toe," Av. angušta- "toe," from ank- "curved, crooked," cf. Skt. angustha- "thumb," ankah "hook, bent," Gk. angkon "elbow," angkura "anchor," L. angulum "corner" (E. angle), Lith. anka "loop," O.E. ancleo "ankle," O.H.G. ango "hook," PIE base *ang-/*ank- "to bend"; → diamond.
The most stable carbon compound with an average particle size of about 5 → nanometers (50 Å). Nanodiamonds are synthesized by detonation of → T.N.T. and then gathering the soot that remains from the explosion.
Fr.: diamant de choc
Any of a series of rings/disks that are formed in a jet flow exhausting a → nozzle when there is a huge difference between the exit pressure and the ambient pressure. At sea level, the exhaust pressure might be lower than the thick atmosphere. In contrast, at very high altitudes, the exhaust pressure might be higher than the thin atmosphere. Shock diamonds can appear just as a rocket is taking off, or at high altitudes when it shifts into → supersonic speed. Shock diamonds are also known as Mach diamonds, → Mach disks, Mach rings, doughnut tails, or thrust diamonds.