Amethyst — specimen 0193, photo © NMNHS
Weight: 8.68 ct; size: 14.92 | 11.22 | 7.86 mm; shape: octagon; colour: medium dark violetish blue; strong; clarity: eye clean; cut: very good; treatment: none.
Very clean specimen; very good 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.