Amethyst — specimen 0368, photo © NMNHS
Weight: 0.83 ct; size: 6.30 | 6.26 | 3.99 mm; shape: octagon; colour: medium violetish blue; very slightly greyish; clarity: eye clean; cut: excellent; treatment: none.
Very clean specimen; design ‘Eight’ by Glenn & Martha Vargas, excellent cut 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.