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Identity Helpproper terminology of this crystal growth

9th Aug 2015 15:29 UTCMichael Otto

06237590016094809607935.jpg



Is there a specific terminology for this type of crystal growth on this 9cm. Smoky Quartz crystal I collected in Connecticut? Most of the crystals I collected from a large pocket had this look. Some also were "phantoms". Am I correct in assuming that this is caused by interruptions of the growth of the crystals?

11th Aug 2015 01:15 UTCReiner Mielke Expert

It looks to me like regrowth on an etched or broken surface.

11th Aug 2015 03:23 UTCWayne Corwin

Is it just on one side, or all the way around?

11th Aug 2015 12:34 UTCMichael Otto

09878340016094809602806.jpg

02040260015661636981518.jpg
All the faces have this same appearance. Here's a couple of different sides not shown in first pic. Thanks for your input. I wasn't sure the proper term that decribes this.

11th Aug 2015 12:59 UTCEligiusz Szełęg Expert

Looks like dissolution figures.

11th Aug 2015 14:11 UTCAmir C. Akhavan Expert

Triangular hillocks pointing upwards and well separated little rhombohedral faces ("miniature tips") usually indicate growth on the rhombohedral faces, but there was some period of either dissolution or growth inhibition by more or less selective deposition of some material that got dissolved later.

A former period of dissolution is more likely, as you can see some patterns of regrowth on the prism faces, too.

Growth did not resume for a long enough time for complete faces to form.


I don't know a "proper terminology" for this.

11th Aug 2015 15:06 UTCWayne Corwin

Verry Cool !


Looks like it had a rough life,,,, Cracked, Etched and Re-Grown,,,, but it's made it "Better" ;-)


Not sure what to call it, but would like to see more of the crystals from that pocket Michael (tu)


Wayne

11th Aug 2015 22:59 UTCMichael Otto

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01906560017055983987530.jpg

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Wayne, Here's two more from the same pocket. They are both @9cm and exhibit the same type growth. In the first photo, the lower right hand side shows a void which seems to indicate Amir's theory of dissolution. The second photo which I know is blurry shows another side of the crystal in the first pic which shows two voids which again may prove Amir's and Eligiusz's conclussion. The third photo is another specimen from the same pocket exhibiting the same appearance. Thanks again for all the replies and furthering my understanding of what I have collected.

12th Aug 2015 00:49 UTCWayne Corwin

Thanks Michael :-)

15th Aug 2015 13:08 UTCHarold Moritz 🌟 Expert

Yeah, definitely a crystal that was etched or dissolved at one point and then grew new crystal faces. There isnt really a term for that. It very commonly happens to quartz crystals in pockets as the chemistry in there changes over time. Crystals will shatter from pressure changes, too, and then new quartz faces will grow over fragments with faces crystalographically aligned with the core fragment. This leads to some really weirdly shaped "distorted" crystals. In Conn. this happened to quartz at Strickland, Gillette, Fillow, and Morris Dam quarries.

15th Aug 2015 13:51 UTCWayne Corwin

Michael


Whats the black in the hole in pic #3960?

Those holes look more like 'casts' from another mineral, not etched, maybe calcite?

17th Aug 2015 08:24 UTCGregg Little 🌟

Michael;


Photos 3960 and 3962 both appear to be leached voids of crystals that the quartz grew over, as Wayne has stated. As stated earlier there is lots of evidence of leaching and regrowth on the quartz indicating a complex diagenetic history in this system. Lots of time for various minerals to come and go which would be only evidenced by molds and casts in the crystals remaining. As far as a term for the regrowth goes, we have a term in the oil industry where secondary quartz void fillers (i.e. cements) re-grow in crystallographic continuity with quartz sand grains and that is simply called "quartz over-growths".

18th Aug 2015 21:28 UTCMichael Otto

02805980016094809622958.jpg
Wayne Corwin Wrote:

-------------------------------------------------------

> Michael

>

> Whats the black in the hole in pic #3960?

> Those holes look more like 'casts' from another

> mineral, not etched, maybe calcite?




Wayne, Here's a better photo of that void in the crystal. Harold, there definitely was some of the explosive shattering in this pocket. One large smoky on the bottom of the pocket was completely shattered on one half but still in place in needlelike pieces but the other half was perfect. All of the crystals had tiny "scratches" on some faces all in the same direction like an explosion caused it. I used to wonder if the some of the energy from the blasting had found it's way into the pocket through a seam and caused the scratches, but Harold's explanation would lead me to believe a natural event caused them. I guess a number of things were going on in there over a very long time.

18th Aug 2015 22:06 UTCBob Harman

The appearance of the immediately previous photo closely resembles the appearance extremely commonly seen in quartz geodes from the American Midwest. The quartz crystal tips point inward towards the central cavity. Within the cavity a corroding calcite seems to exist. Within the deep surrounding crevices bits of dirt, organic matter and lichens are seen as the very thin dark streaks.

Put some vinegar or other acid into the cavity and see if you can etch out the calcite. Then try cleaning with a hi pressure cleaning gun and you should really freshen up the specimen. If the central grayish corroded crystal doesn't react with the acid, it probably is a broken and corroding portion of the quartz lining.

I think it is all natural……no "blast" or other type of artificial creation of the cavity to my eye. CHEERS……BOB

19th Aug 2015 06:35 UTCGregg Little 🌟

Michael;


You wrote ... "All of the crystals had tiny "scratches" on some faces all in the same direction like an explosion caused it." ...


One thing to keep in mind is that these veins, with the wonderful crystal deposits we seek, are typically part of a fracture system caused by faulting. If the faults are active during crystal formation then breaking and crystal regrowth would happen and could give the appearance of scratches and faces all in the same direction.

19th Aug 2015 13:56 UTCHarold Moritz 🌟 Expert

If these quartz specimens are from where I think, then they are from a miarolitic cavity in a pegmatite, rather than a brecciated, fault-hosted vein. There is rarely calcite in these cavities, but of course calcite is common in fault veins and geodes and the processes described above for those latter geoenvironments are quite valid. Thus always good to post the specimen's geoenvironment to aid in these discussions. It might be difficult to distinguish between geologic pocket collapse and damage from blasting if both have occurred. But overgrowths, which can be very subtle, can only happen when the pocket is still deep in the ground and at high temps so fragments without them are more likely from blasting.


Quartz overgrowths are common in veins also, producing wonderful things like sceptered crystals if conditions allow, and as mentioned, create the "cement" holding quartzite (a really tough rock!) together by filling the pore spaces in the original sandstone. Thinking about it more, the subparallel quartz crystals found lining many fault veins cutting quartzite (or other quartz-rich rox) are also overgrowths in the sense that they originate from the broken quartz grains on the fault walls that happen to have their c-axes nearly perpendicular (normal) to the fault wall. If there is silica in the hydrothermal solution in the fault (nearly always so), then new quartz overgrows all the exposed grains. But only those grains with the proper (normal) crystallographic orientation will result in long crystals that can project far out into the open fault space. Grains with their c-axes not normal to the walls will butt up against other quartz crystals before they get very far. If the Earth's crust had no other mineral than quartz, there would still be many fun things to collect!
 
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