Birthstones by month: a guide for gift buyers

The table below follows the lists published by GIA and the American Gem Society (AGS). They agree on almost every stone. The difference is sardonyx: AGS lists it for August, and the GIA page does not. Both list bloodstone for March.

Birthstone lists are not fixed. In AGS's account, sardonyx was August's original stone, then peridot was added, and in 2016 August joined June and December as a month with three stones, spinel being the newest of them. If a month has several stones, any of them is a correct birthstone, so you can choose the one that suits the piece.

Hardness figures are on the Mohs scale, as stated on AGS's pages for each stone. The 9 for ruby and sapphire comes from AGS's spinel page, which compares spinel with them, and where AGS gives no number at all, the table repeats its wording instead of guessing.

Hardness on the Mohs scale describes how well a stone resists scratching. It is the first thing to check, but it is not the whole story. Topaz is a hard 8, yet its perfect cleavage can make it prone to chipping or cracking unless it is cut well. Zircon measures 7.5, but AGS flags that its faceted edges can chip. Opal is delicate for a different reason: Its water content, combined with a hardness of only 5.5 to 6, means it can crack or craze under extreme temperature, dehydration or direct light.

The piece matters as much as the stone. A ring takes knocks every day, while an earring or pendant sits away from doors, counters and keyboards. A soft stone that scratches quickly on a ring may stay in good shape in earrings, which take fewer knocks.

Ruby and sapphire (both 9) are among the most durable gemstones and suited to daily wear. Diamond is the hardest, and spinel, at 8 with no true cleavage, is described by AGS as strong against cracks, chips and breaks. Alexandrite, at 8.5, is durable enough for regular wear with proper care. Aquamarine (7.5 to 8) is also a sound choice.

A second group is wearable with ordinary care: amethyst and citrine at 7, bloodstone at about 7, tourmaline at 7 to 7.5, and garnet at 6.5 to 7.5. Tourmaline is very wearable.

The softer stones need more thought for a ring. Peridot and sardonyx (both 6.5 to 7) are best worn in earrings or necklaces unless they sit in a protective mounting, and tanzanite suits earrings and pendants better than rings. Turquoise tops out at 6 and is vulnerable to sunlight and to solvents such as makeup, perfume and natural oils. Emerald, pearl, moonstone and opal all need careful wear.

Setting changes the odds. In GIA's guide, a bezel setting protects the stone around its edge and resists chips and everyday wear, while prongs let in more light but should be checked from time to time. The engagement ring settings guide compares them in more detail.

Match the stone to the knocks the piece will take.

• Earrings: the safest place for the softer stones. Peridot, tanzanite, sardonyx, opal, pearl and moonstone all work here, as long as you can accept a little extra care.
• Necklaces and pendants: also gentle on a stone. Necklaces are a good home for peridot and sardonyx.
• Bracelets: a wrist hits tables and door frames, so lean toward stones of about 7 and up. Peridot and sardonyx (both 6.5 to 7) are a good option for occasional wear in bracelets, so save those for dressier days.
• Rings: choose from ruby, sapphire, spinel, diamond, alexandrite and aquamarine for daily wear, or any softer stone for occasional wear in a protective setting.

If the stone matters more than the piece, a jeweller can design around it. Custom jewellery design lets you pick the stone first and then choose a setting that protects it, and the design studio is where that conversation starts.

Many coloured stones are enhanced, and that is usually accepted when it is disclosed. Most commercially sold tanzanite is heat-treated, aquamarine is often heat-treated to improve its blue, and most citrine on the market is made by heating amethyst or smoky quartz. It says blue topaz very rarely occurs naturally and is often caused by irradiation treatment. Many emeralds are treated with oils to improve clarity, which is common and accepted, and high-quality unheated sapphires can command exceptional prices.

The practical step is to ask what, if anything, has been done to the stone, and how to clean it, since some treatments change the right cleaning method. AGS's advice is to check whether an aquamarine has been fracture-filled before using ultrasonic or steam cleaning. The jewellery care guide covers everyday cleaning.

April's diamond comes as a natural diamond or a lab-grown diamond, and diamond treatments are a separate topic worth understanding before you buy.

You have more room than most gift guides suggest. Months with several stones let you choose: in June, alexandrite (8.5) is harder than pearl or moonstone; in August, spinel at 8 is harder than peridot; in October, tourmaline is harder than opal; and in November, topaz at 8 is harder than citrine at 7. If a colour is not to their taste, the same month often offers a different hue.

You can also give a stone from a different month entirely. Birthstones are a tradition, not a rule, and the traditions around them differ by culture and by list. Many sources attach powers to particular stones, but those are beliefs and stories, not properties of the gem, and a gift does not need them.

If the piece is for a special occasion, allow time. A custom diamond ring takes about four to six weeks, so start well before the date, and the custom engagement rings page explains the process. You can also see how a stone looks on the hand at one of the showrooms.