Quartz-beta

A high-temperature (> ~573°C) polymorph of silica with a crystal structure very similar to that of quartz ("alpha-quartz"), but with a higher symmetry (beta-quartz: hexagonal, quartz: trigonal; Bragg and Gibbs, 1925; Heaney, 1994). Like quartz, beta-quartz occurs in left- and right-handed crystals.

It is not considered a formal mineral species by the IMA. Their structures have the same topology, so alpha- and beta-quartz are polymorphs, but not different species (Nickel and Grice, 1998). As it is not stable at room temperature and cannot be quenched from high temperatures. All "beta-quartz" or "quartz-beta" or "high quartz" in collections actually represent paramorphs of quartz after beta-quartz, or is simply just bipyramidal quartz crystals . This is why on Mindat there is not a single photo labelled "quartz-beta", they are all labelled quartz.

The phase transition is at about 573°C at ambient pressures. When heated quickly, beta-quartz melts at about 1550°C, otherwise it will turn into beta-cristobalite at around 1050°C. The temperature of the phase transition from quartz to beta-quartz increases with pressure.



"Beta-quartz" is most commonly found in silica-rich volcanic rocks like rhyolite, in which it occurs as stubby, bipyramidal and usually dull and gray crystals/paramorphs embedded in the matrix. This has led people to believe that quartz crystals with a bipyramidal habit from other, non-volcanic localities grew as beta-quartz, and the habit is unfortunately called "beta-type" or similar.

However, "beta-quartz" that grows freely in cavities frequently forms elongated crystals that are very similar to quartz, or even as very thin, needle-like crystals Eg: https://www.mindat.org/photo-214061.html