This Sevastopol-dug Crimean War relic dates ca.1855, and ostensibly belonged on the piper's coatee. It's rhomboid, 2 cm-long on each side, in uncleaned state. The shank is missing. Button was fabricated by Gilpin.
This is a nice memento from the brave 93rd (Sutherland Highlanders) Regiment of Foot, which was immortalized in the Thin Red Line. This rhomboid button was in use by the Highlanders for only 2 years, in the Crimean War and during the Indian Rebellion of 1857, and was soon replaced.