Discussions

╳Discussions

Groups

Recent Images in Discussions

GeneralThe impressions on the crystal surface of today's POTD

24th Nov 2014 09:35 UTCHenri Koskinen Expert

In the description of the POTD Rock Currier asks how the impressions can be explained.

http://www.mindat.org/photo-646459.html

Here is a set of photos that could explain how the markings in POTD's crystal surface were born.

Markings on crystal surface similar to the markings in Rock Currier's POTD.

https://farm8.staticflickr.com/7534/15680980107_b56581f91b_o.jpg Birth of inclusions by Henri Koskinen, on Flickr

Wider view which shows that the markings are related to mineral growth on the crystal surface. Here the underlying crystal is fluorite and the growth on the crystal face is probably some kind of iron oxide.

https://farm8.staticflickr.com/7523/15589990648_d91c9d853d_c.jpg Fluoriittia Kemiön Illosta by Henri Koskinen, on Flickr

Inside of an inclusion: the core and spere. There must be a reason for this geometrical structure but I don't know what the rules here are.

https://farm9.staticflickr.com/8644/15840933946_a50cb32970_o.jpg Birth of inclusions by Henri Koskinen, on Flickr

Looks like the shape and size of the inclusion depends on

-where on the crystal face the inclusion has formed (ace, corner or edge)

-what are the relative growth rates of the inclusion and the crystal faces

https://farm8.staticflickr.com/7498/15866752195_3c99a65da5_o.jpg Birth of inclusions by Henri Koskinen, on Flickr

https://farm9.staticflickr.com/8623/15680741109_816fda08be_o.jpg Birth of inclusions by Henri Koskinen, on Flickr

Looking at these photos suggests that the markings in Rock Currier's POTD could well be due to similar process. There has been a secondary growth on the quartz crystal surface. The growth of the quartz crystal surcface has stalled fairly soon after the birth of the secondary growth (here some hexagonal mineral). Then the secondary growth has been erased (maybe machanically or by leaching) and all that is left is the impressions on quarts surface showing the geometry of the erased secondary growth.

Henri

24th Nov 2014 17:34 UTCUwe Kolitsch Manager

The imprints could be due to later dissolved hexagonal crystals (e.g., apatite) - this would produce both square (prism face attached) and hexagonal imprints (basal pinacoid attached). Alternatively, since the hexagonal outline is not fully symmetric, cuboctahedra of a cubic mineral (e.g., pyrite) could be responsible.

27th Nov 2014 21:47 UTCRock Currier Expert

Uwe,

That's the most reasonable thing I have heard yet.