In this article
Written by Sameer
Reviewed on
Black agate costs very little compared with most stones, so it is often the first gem people buy. Cheap does not mean careless, though. A few small details decide how pleased you end up, and the most important one is something many sellers never mention.
Start here: most black agate is dyed
Truly jet-black agate is rare in nature. Most of the black agate and "black onyx" sold around the world began as grey or banded chalcedony and was then colour-treated. The traditional method soaks the stone in sugar and then acid, which carbonises the sugar inside its pores. The black is permanent, it will not rub off, and the trade has accepted it for centuries. The stone is still natural agate; only its colour has been helped along. What counts is that the seller says so and the price matches.
The real fakes: glass and plastic
The substitute to watch for is black glass. Signs to look for:
- round gas bubbles or swirl lines under a loupe or your phone's macro lens;
- it feels cold at first, then warms up very quickly in your palm;
- soft, moulded edges where a cut stone would show crisp facets or a smooth, even dome;
- a weight that seems off, either too light (plastic) or strangely heavy.
Good stone or ordinary stone?
How deep the black goes
Put it under a bright lamp. A better stone looks deep and even all over. A weaker one shows brownish or grey patches, usually near the edges.
The polish
Good polish gives a clear, mirror-like reflection. A hazy surface with an orange-peel texture tells you the stone was finished in a hurry.
Shape
For a ring, a symmetrical oval or cushion cabochon with a flat, smooth base sits better in the setting than a lopsided one. If the listing has a side photo, check it.
Day-to-day wear
Black agate is a type of chalcedony and sits at about 6.5 to 7 on the Mohs scale, so it is fine for a ring you wear every day. Wipe it with a damp cloth and store it away from harder stones that could scratch it.
Three things to get confirmed
- It is natural agate, not glass.
- Any dyeing or colour treatment is written down.
- The weight quoted is the stone alone, not the stone plus the setting.
We check every stone in our black agate collection against those points and photograph each one by itself. If you want something different, look at moh-e-najaf, or move up to emerald. Our gemstone names page lists the Urdu names. We ship from Karachi to Lahore and the rest of Pakistan, and with Cash on Delivery you open the parcel before you pay.
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