Prehnite is a calcium aluminium silicate with a soft, glowing green best described as gooseberry or sea-foam. It has a gentle inner mistiness that jewellers love, and many stones carry fine black needles of epidote or tourmaline that add character. It holds a small place in history as the first mineral ever named after a person, the Dutch colonel Hendrik von Prehn, who brought it back from South Africa in the 1780s. Today the best gem material comes from Mali and Australia.
Prehnite sits at 6 to 6.5 on the Mohs scale, firm enough for regular wear with a little common sense: it prefers pendants and earrings and forgiving settings for rings. It is cut both as glowing cabochons and, when clean, as faceted stones with a soft, velvety look. Keep it away from strong heat and harsh chemicals, and clean it with warm, soapy water. Its misty translucence is quite distinctive, which makes convincing imitations thankfully uncommon.
Other beautiful green gems, though prehnite's misty green glow sets it apart.
