Crystals of silica are known as quartz. Pure quartz is colourless and known as rock crystal. If a small amount of iron is present as an impurity, the colour may be purple (amethyst) or yellow (citrine). Sometimes quartz contains aluminium and by a process of natural radiation in the Earth, becomes smoky grey or brown in colour. This is known as ‘smoky quartz’. Amethyst is a variety of quartz, one of the most common minerals in the Earth's crust.
This ring forms part of a collection of 154 gems bequeathed to the V&A by the Reverend Chauncy Hare Townshend, a cleric and poet. Sir A. H. Church gave additional specimens in 1913. He also compiled the first catalogue Precious Stones: A Guide to the Townshend Collection. The first edition appeared in 1883. The stones are mounted as rings, although they may not have been intended to be worn.
Some of these, including this amethyst, were originally owned by Henry Philip Hope, a brother of the novelist and antiquary Thomas Hope. H. P. Hope formed a famous collection of diamonds and precious stones which was largely inherited by his three nephews. His collection included the Hope blue diamond, now in the Smithsonian Institution, Washington.