Highgrade ore is exceptionally rich. To highgrade a mineral collection is to sort out the best specimens. Highgrading in the mining industry means either removing only the best ore or, more commonly, theft by miners. Halite, pyromorphite, vanadinite, and galena often form hopper crystals. One mineral occurring within another.
Inclusions can also be liquid or gaseous.
These are highly desirable, for example a quartz crystal with a pyrite crystal included is of far more interest than an unincluded quartz crystal. Japan law twin A pair of quartz crystals, typically formed in a flattened v-shape, joined at an angle of 84 degrees 30 minutes. Specimens sold wholesale, from one dealer to another, are keystoned. Interestingly enough, the specimens are occasionally doubled in price before being keystoned. An exceptional specimen.