Talk:Opal/@comment-26343489-20160108231218/@comment-25116934-20160117231942

It's not too difficult when you think about it. A hexagonal facet means it's faceted into a hexagon shape. A dipyramid (or bipyramid) is 2 pyramids connected at their bases. A hexagonal dipyramid is thus a dipyramid, but in a hexagonal shape. A hexagonal dipyramid has 12 triangular faces, 8 vertices, and 18 edges.

To truncate something is to cut it off by it's top. So, when you look at Amethyst's gemstone, it's basically a hexagonal dipyramid with the pointy parts sliced off. You can look up "truncated hexagonal dipyramid" in google images or something, and you'll probably see a picture of Amethyst's gem.

I love solid figures.