Amethyst — specimen 0612, photo © NMNHS
Weight: 0.91 ct; size: 6.75 | 6.64 | 4.44 mm; shape: round; colour: medium violetish blue; very slightly greyish; clarity: eye clean; cut: excellent; 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.