Amethyst — specimen 0218, photo © NMNHS
Weight: 5.08 ct; size: 12.53 | 8.38 | 8.06 mm; shape: octagon; colour: light bluish violet; very slightly greyish; clarity: eye clean; cut: excellent; treatment: none.
Very clean specimen; angles [skipping after 45 in the crown] as in ‘Opposing Corners 15’ by Robert H. Long, 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.