Diamond is the hardest natural material. The Mohs hardness scale, on which diamond is a '102 and corundum (sapphire) is a '92, doesn't adequately attest to this incredible hardness, as diamond is exponentially harder than corundum. Diamond is also the least compressible and stiffest substance. It is an exceptional thermal conductor - 4 times better than copper - which gives significance to diamonds being called 'ice'.
Diamond has an extremely low thermal expansion, is chemically inert with respect to most acids and alkalis, is transparent from the far infrared through the deep ultraviolet, and is one of only a few materials with a negative work function (electron affinity). One consequence of the negative electron affinity is that diamonds repel water, but readily accept hydrocarbons such as wax or grease. Diamonds do not conduct electricity well, although some are semiconductors.
Diamond can burn if subjected to a high temperature in the presence of oxygen. Diamond has a high specific gravity; it is amazingly dense given the low atomic weight of carbon. The brilliance and fire of a diamond are due to its high dispersion and high refractive index. Diamond has the highest reflectance and index of refraction of any transparent substances. Diamond gemstones are commonly clear or pale blue, but colored diamonds, called 'fancies', have been found in all the colors of the rainbow.
Think of a circle. It has no beginning or end. Think of a knot tied around your finger. It binds and reminds. And so it is with a ring. It reminds you of an eternal binding commitment to a lover, spouse, friend, school, church, club, or country.
The commitment to marry a woman is usually expressed by placing a ring on her fourth finger. This custom might have originated with the Egyptians. They believed a special vein or nerve ran from that finger to the heart.
Another explanation for the custom is that it may have been a suggestion to women that they should be submissive to their future husbands since the fourth finger is the weakest one and can't be used independently. A third explanation is that placing the ring on the fourth finger may have been a way to avoid damaging the ring since it is the best-protected finger.
Diamonds were probably first added to wedding and engagement rings in the 15th century.
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