April Birthstone: Diamond

• Diamonds are graded on the 4Cs, a system GIA developed in the 1950s: color, clarity, cut and carat weight.
• On the usual color scale, from colorless to light yellow or brown, colorless diamonds are the rarest and most valuable. Cut decides how light moves through the stone, which gives its brightness and fire.
• One carat is 0.2 grams.

• Lab-grown diamonds have the same crystal structure as natural diamonds and nearly the same chemical, optical and physical properties. Ordinary gem tests cannot tell them apart; a gem lab or advanced instruments can.
• GIA grades lab-grown diamonds on their own report and laser-inscribes each one with the report number and a note that it is laboratory-grown.
• Simulants such as cubic zirconia, moissanite and glass only look like diamond. They are different materials, and a jeweler can identify them easily.

At 10 on the Mohs scale, diamond is the hardest gem, and GIA calls it the most durable of all gemstones, which is why it is the classic stone for a ring worn every day.

• The first diamond engagement ring on record was given by Archduke Maximilian of Austria to Mary of Burgundy in 1477.
• The largest diamond ever found, 3,106 carats, came from South Africa's Premier mine in 1905.

• Warm, soapy water and a soft brush: always safe.
• Ultrasonic cleaner: usually safe, but not for stones with many inclusions or treatments.

For heavily included or treated diamonds, use warm water, mild soap and a soft toothbrush, or a lint-free cloth.