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Identity HelpHexagonal dipyramidal Quartz?

24th Jan 2020 13:43 UTCPelopidas Lympouris

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Found a rock at Phyti village, Kathikas Complex, Paphos Cyprus that is FULL of this crystals.. 
most of the crystals (and there are A LOT of them) are “floaters” with different sizes, perfect hexagonal dipyramidal, some are transparent, some are greyish/bluish color and there are others that when light hits them are yellowish.. some are 1.5cm and some are very tiny but u can hold them in ur fingers.. 
After a quick search i found that they are Quartz after β-quartz.. 
is that right? What other informations can u give me about those?
I’ve read that they form at higher temperatures and crystalize inside a liquid magma.. correct?
most of them are trapped inside a blueish/greenish mud (i assume that this was the magma?).. and some are trapped inside calcite.. 
I’m using HCI to etch calcite to expose the crystals..
There is a black mineral on the rock which i assume is goethite?
Are they a rare occurrence?
Thank u all!

24th Jan 2020 13:44 UTCPelopidas Lympouris

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The whole rock..

24th Jan 2020 13:45 UTCPelopidas Lympouris

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Photo2

24th Jan 2020 13:46 UTCPelopidas Lympouris

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Photo 3

24th Jan 2020 13:48 UTCPelopidas Lympouris

Forgot to take a picture of the black mineral.. when i get back home I’ll post a photo of it aswell..

24th Jan 2020 16:26 UTCBob Harman

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Dipyramidal quartz crystals (also sometimes called bipyramidal quartz crystals) are uncommon, but not rare in a Midwest sedimentary type geode variety called "dew drop diamond" geodes (because the individual quartz crystals sparkle like dew drops in bright sunlight).    The quartz crystals are small, generally being 2 mm - 4 mm in size. The Midwest quartz geodes are  low temperature deposits.

Here is one of multiple examples from my collection. The largest dominant crystal,  seen  in the left half of the geode, is 4 mm.     CHEERS......BOB

27th Jan 2020 09:59 UTCPelopidas Lympouris

Oh my.. this is so beautiful!! Thank u Bob!

24th Jan 2020 16:40 UTCErik Vercammen Expert

Quartz formed above 573°C is really hexagonal. On cooling, the structure of these crystals convert to trigonal, but the external form stays the same.
But there is also the possibility that these crystals are formed beneath that temperature, and with a trigonal structure: see "cumberland habit" for these crystals.

27th Jan 2020 10:00 UTCPelopidas Lympouris

I think u r right Erik! This is indeed a Cumberland habit! Thank u!

24th Jan 2020 16:46 UTCHarold Moritz Expert

Beta quartz is a high-temperature phase of silica (see mindat glossary) and its crystals are not limited to the habit you found, so that is not it. What you have is regular quartz, in this case crytallized in the quartzoid or Cumberland habit, a habit that forms at low temperature. Common in geodes, vesicles in basalt, brecciated fault rocks and so on.

27th Jan 2020 10:01 UTCPelopidas Lympouris

Thank u for the info Harold! I’ll keep this in mind! I’ll do more research next time!:)

24th Jan 2020 17:06 UTCUwe Kolitsch Manager

Fully agree with Harold.

24th Jan 2020 20:22 UTCAlfred L. Ostrander

As Harold has mentioned, it appears these crystals are low temperature quartz and are often referred to as the Cumberland habit due to the lack of a prism. To remain true to crystallography the symmetry of low temperature quartz is trigonal as found in the trigonal trapezohedral class. As such, the forms present are not that of the hexagonal dipyramid but that of the positive rhombohedron r{10-11} combined with the negative rhombohedron z{01-11}. For further reference, check out the articles on crystallography that Don Peck and I wrote for Mindat. 
Thank You,
Alfred L Ostrander

27th Jan 2020 10:07 UTCPelopidas Lympouris

I’m  new to this Alfred and still learning.. I’m a Surveyor and have little knowledge of geology (geology classes at the University) but i know nothing about crystallography! I’ll make sure I’ll read the articles! Thank u!

25th Jan 2020 03:48 UTCMatthew Droppleman

Nice shape!

27th Jan 2020 10:15 UTCPelopidas Lympouris

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Yea they r beautiful! In this picture notice the transparent yellowish crystal in the middle.. further up right there are smaller black ones with perfect shape!  Bottom of the picture is a cluster with bigger crystals! I do like quartz crystals and their  different formations!

27th Jan 2020 13:14 UTCHarold Moritz Expert

There's a lot to love and learn about quartz! Check out this site:
BTW, any time one sees a Greek letter in front of a mineral name, that tells them it is a "material" name and not a mineral name.  The Greek letters are used in material science to denote different crystallographical phases of the same chemical material that are stable at different pressures and tempertures. If one of those phases also occurs in nature, then it will get a separate mineral name (e.g., quartz, tridymite, cristabolite) (they are polymorphs, the same as kyanite, sillimanite and andalusite). In the case of quartz, the mineral names predate the material studies, so the mineral name is used as the root. But if it was purely artificial, then the phases would be called "alpha-silica", "beta-silica", etc. Most of the phases studied for many materials do not occur (or have not been found yet) in nature, or in the case of beta-quartz are not stable at surface conditions, they are lab grown, or theoretical - minerals have to be natural.

27th Jan 2020 16:00 UTCD Mike Reinke

Harold,  thank you for that explanation of the meaning of the Greek letters. I haven’t found anything on that in the things I’ve read in my spare time. Offhand, can you recommend a article or a chapter in a book that goes into more detail?. Thanks.
 
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