Smoky quartz is a popular gemstone and rock-shop item. There's just something more interesting about a dark quartz spear than the clear "rock crystal" variety. A few months ago, I picked a spear out of an assorted box of smokies and have had it on my desktop (the real one) since then. Today I took its portrait and made sure to show off its root-beer brown color, the feature that qualifies it as not just smoky quartz, but cairngorm. See it at closer range in the Quartz/Silica Mineral Gallery.
Cairngorm Geology Guide photo