Amethyst — specimen 0224, photo © NMNHS
Weight: 3.40 ct; size: 10.98 | 7.82 | 5.57 mm; shape: octagon; colour: medium violetish blue; very slightly greyish; clarity: eye clean; cut: excellent; treatment: none.
Very clean specimen; excellent step cut style by Tan Pen.
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.