Pink Beryl and Emerald Crystals
Emerald is actually a member of the beryl family of gemstones (including aquamarine, heliodor, red beryl, and others), but with a higher number of impurities (known as inclusions), and colored various shades of green by trace amounts of chromium.
While dozens of questionable cures and wards for the plague are known, the royalty of both Europe and Byzantium believed that crushed emerald was the surest ward, and would save them from any plague-related death. This belief went so far as to lead the apothecaries and physicians of sixteenth-century England to release a declaration stating that the inefficacy of gems in both curing and warding the plague was due to improper identification and preparation of gems prescribed, not because the “cure” was simply a ploy on the nobility’s belief that the more expensive something was, the better it was.
A Book of Precious Stones. Julius Wodiska, 1909.