Choosing a gemstone for a ring you wear every day

Hardness first. On the Mohs scale, diamond is 10. Ruby and sapphire, both corundum, are 9. Emerald, aquamarine and morganite, all varieties of beryl, are 7.5 to 8.

Toughness is separate. Diamond is the hardest, but it has cleavage directions, where a hard blow can split it. Ruby and sapphire have excellent toughness and no cleavage. Emerald’s toughness is fair to good, and nearly all emeralds have fractures. Morganite is more likely to chip than harder gems, and aquamarine is durable when it is protected from scratches and hard knocks.

Color, and often a birthday. Ruby is the birthstone for July, sapphire for September, emerald for May, aquamarine for March and diamond for April.

The softer and less tough the stone, the more its setting matters. Ruby and sapphire can be worn every day. Emerald and morganite do best in a protective setting, such as a bezel or a halo, for daily wear. Aquamarine is durable when it is protected from scratches and hard knocks.

Ask about treatment. Heating is the common treatment for ruby and sapphire; most emeralds are filled with oils, resins or polymers; most aquamarine is heat-treated to a purer blue; and morganite almost always is, to improve its pink. Ask, too, whether a stone is natural or laboratory-grown.

For a ring worn every day with the least to think about: diamond, ruby or sapphire. For emerald, aquamarine or morganite: a setting that protects the stone, and a ring taken off for hard work.

The Design Studio offers natural and lab-grown diamond; blue, pink, yellow and white sapphire; ruby; emerald; morganite; and aquamarine, from 4 to 12 mm long, and shows each stone’s approximate weight from its own density. By the studio’s figures, corundum (specific gravity 4.0) weighs about 1.1 times a diamond (3.52) of the same size, and beryl (2.72 to 2.8) about three quarters to four fifths.

For any stone: its size, its color and clarity, any treatment, and whether it is natural or laboratory-grown; then the metal and the setting. Sara quotes the finished piece after a consultation.

Warm soapy water and a soft brush are safe for every one of these stones. Ultrasonic and steam cleaners are usually safe for an untreated or heated ruby or sapphire, but not for one that is fracture-filled, cavity-filled or dyed; they are risky for emerald; and aquamarine and morganite are usually fine unless the stone has liquid inclusions or fractures. For diamonds, GIA doesn’t recommend harsher methods at home.