Turquoise & Quartz, from Fort Lismeenagh (Ballycormick), Shanagolden, Limerick County, Munster, Ireland (REF:RSB6)

Turquoise is a cooper aluminium phosphate mineral. Its striking blue colour is caused by copper, and the greenish shades of Turquoise are because of iron. Its crystal structure is triclinic, and it is usually composed of submicroscopic crystals, making the stones opaque.

The name Turquoise is derived from the French pierre turquoise, meaning ‘Turkish stone’. This is because the trade routes through which Turquoise reached Europe from the mines in central Asia went through Turkey, and Venetian merchants often bought the stones in Turkish bazaars.

Turquoise may be the longest-used of all gemstones. Beads dating back to 5000 B.C. have been found in Iraq. The Egyptians were mining Turquoise in the Sinai in 3200 B.C. Throughout history, Turquoise has been fashioned into jewellery and decorations for a host of objects, from weapons to amulets.

Turquoise is the national gemstone of Iran, and it has been the most valued gem in Tibet for many centuries. About 1,000 years ago, Native Americans began to mine and fashion Turquoise, and the gem has been found in burial sites from Argentina to New Mexico.