Amethyst — specimen 0091, photo © NMNHS
Weight: 2.21 ct; size: 8.88 | 8.86 | 5.60 mm; shape: round; colour: medium dark violetish blue; strong; clarity: eye clean; cut: very good; treatment: none.
More information from ‘Classification’
A violet variety of quartz. The colour is caused by iron impurities in the 10s to 100s parts per million range.