Amethyst — specimen 0402, photo © NMNHS
Weight: 0.76 ct; size: 7.04 | 6.02 | 3.81 mm; shape: oval; colour: medium violetish blue; very slightly greyish; clarity: eye clean; cut: excellent; treatment: none.
Very clean specimen; design ‘Ovalimixtum ST’ [culet facet added], 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.