Aquamarine and emerald are varieties of the mineral beryl. The colours are caused by chemical impurities. Traces of chromium create the green of emerald, and traces of iron cause the greenish-blue of aquamarine. Greenish-blue aquamarine can also be heated to create a more intense blue colour.
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 acquamarine, 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.