FMF - Friends of Minerals Forum, discussion and message board

[John S. White]

This is a classic Cumberland habit quartz, which mimics the shape of beta quartz crystals, but it is indeed alpha or low temperature quartz. A close inspection will reveal that alternate pyramid faces are not the same size and this is also true of the corresponding narrow prism faces, characteristics that definitely deny this being a beta quartz crystal.


Rob Lavinsky photo

[Aymeric]

My, I thought I had a nice Czech Béta Quartz specimen until I read this thread.

Was I wrong ?

[John S. White]

Sorry to say it appears that you are wrong. What you appear to have is a very nice Cumberland habit quartz from the Czech Republic.

Welcome to the Forum, we are very pleased to have you join us.

[Pete Richards]

Quartz very similar to the Cumberland specimen posted by John White is also found, again on hematite, at Chub Lake, New York. Similar crystals, without the hematite, are found in ironstone concretions in the Huron River valley in northern Ohio. In both cases these are alpha quartz.

Actually, even beta quartz is not beta quartz. Beta quartz only exists at high temperatures (above about 570°C). Below that temperature, the structure shifts slightly to that of alpha quartz, so crystals that started out as beta quartz become complex intergrowths of alpha quartz domains that are twinned relative to each other according to the Dauphiné twin law. The transformation is a very easy one, since it does not require breaking any chemical bonds, and thus it takes place quickly and reliably once the appropriate temperature is reached.

The believable "beta" quartz examples I have seen are frosted on the crystal faces and translucent. Apparently beta quartz most commonly grows as crystals within a lava - phenocrysts - although it sometimes grows in cavities in rhyolites as well.

[Aymeric]

No need to be sorry John, I might be wrong, but at least I've learned something ! now I know what a Cumberland habit is, thank you !

[marco campos-venuti]

Hi all, nice theme!
This is a specimen of the "Porfido granodioritico" from Elba Island, Italy. It is a magmatic body of granodiorite characterized by big phenocrystals of orthoclase (not in this sample) and phenocrystals of quartz, associated to the main body of the Monte Capanne pluton, famous for its pegmatites with elbaites.
In the specimens the quartz crystals are partially freed from its magmatic matrix due to wind erosion.
If I understand well, this can be a beta quartz (alpha pseudo after beta). The symmetry is strictly hexagonal, but the prism is present.

[John S. White]

Beta quartz crystals can exhibit prisms, no problem. Your crystals do appear to be pseudomorphs after beta quartz.

[Pete Modreski]

Thank you for showing us this particularly good specimen, Marco. It's very unusual to see the beta quartz* crystals well exposed on the matrix this way!

*and we all will understand, of course, that if I write "beta quartz" for brevity, I really mean "alpha quartz paramorphs after beta quartz".