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Identity Helpproper terminology of this crystal growth
9th Aug 2015 15:29 UTCMichael Otto
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
11th Aug 2015 03:23 UTCWayne Corwin
11th Aug 2015 12:34 UTCMichael Otto
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
11th Aug 2015 14:11 UTCAmir C. Akhavan Expert
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
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
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
15th Aug 2015 13:08 UTCHarold Moritz 🌟 Expert
15th Aug 2015 13:51 UTCWayne Corwin
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 🌟
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
-------------------------------------------------------
> 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
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 🌟
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
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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