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| Length of crystal ~1.7 cm |
At a small venue in Tucson I stumbled upon an
interesting specimen labeled “red quartz.”
I immediately shelled out a couple of bucks since it was a doubly
terminated, nice floater crystal, and it was red. It seemed obvious the
crystal was authigenic quartz since it had sharp hexagonal crystal faces with
simple terminations. It “looked”
essentially identical to the authigenic quartz known as Pecos Diamonds (see
Blog posting July 11, 2013) except for the red color. The red specimen came from a well-known
collecting locality at Domeño,
Chelva, Valencia, Valencian Community, Spain (www.mindat.org). Here the Triassic Keuper Formation produces floater
red quartz crystals from gypsum bearing marls.
The Triassic Period (~252-201 Ma) was named for rocks
exposed in Germany where there is a tripartite division: the Bunter is mostly early Triassic with an
arbitrary boundary with the Late Permian (mostly terrestrial), the Muschelkalk
is Middle Triassic (inland marine with some restricted circulation basins) while
the Keuper is Late Triassic (lots of deposition in evaporitic basins with minor
marine incursions). Much of the Keuper
deposition is related to basins created by the initial breakup of supercontinent
Pangaea---the future North America rifting apart from the future Europe (Laurasia). Rocks of the Keuper (readers will notice that
Keuper is used as a formation/group name as well as a generic name for the Late
Triassic) are exposed over much of Europe including the British Isles. The rocks also were extensively deformed by numerous
Mesozoic and Tertiary orogenies. The terrestrial
sediments of the Keuper are well-known for producing dinosaurs (and numerous
other fossils).
The red colored Spanish quartz is known as ferruginous
quartz, Eisenkiesel, or locally Jacintos de Compostela. The latter name is often used by agencies selling
specimens. The red color is due to inclusions
of hematite scattered evenly throughout the crystals and is different from
other red-colored crystals created by surficial hematite. There are very few localities around the
world that have produced Eisenkiesel and the Spanish locality is certainly the
best known.
So, if readers are interested in collecting
interesting and different specimens of quartz look for Jacintos de Compostelas
at the next rock show.