Anhydrite is a form of calcium sulphate (CaSO4), with almost the same composition as 'Egyptian alabaster', but without water. Anhydrite has also often been called 'blue marble', though not all materials called 'blue marble' are anhydrite. Anhydrite was mostly used in the Middle Kingdom (about 2025-1700 BC), and perhaps the Second Intermediate Period, for making cosmetic vessels.
Aston 1994: 51-53
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