Dark mineral identification

[Paolo997]

Hi,

always from the Omhden (DE) quarry. I'm wondering what this dark mineral actually could be... I'll report 2 different speciments, both about 10-15cm in length. They have little white "spiderweb" across the dark lucid surface. it is like 1mm thick

this could be really useful for beginners like me

 

thanks a lot

Paolo

[Ludwigia]

I think what you may have there is jet. We call it gagat in German.

[Rockwood]

Coal is what came to mind looking at the second one. It seems jet is an underachieving form of coal.  

[Ludwigia]

I'd say it's rather overachieving, since it's classified as a gemstone

[Rockwood]

Wiki calls it among "the lowest rank of coal". Maybe it is an achievement to make gemstone from such humble beginnings . 

[Paolo997]

Super

so it's a sort of fossilized wood like coal, but with slight different process. May i ask what cause these white nets across the mineral?

 

Thanks again

Paolo

[Ludwigia]

26 minutes ago, Paolo997 said:

May i ask what cause these white nets across the mineral?

 

It may be gypsum, which sometimes occurs in this type of deposit.

[Paolo997]

Thanks a lot @Ludwigia

[FranzBernhard]

14 hours ago, Paolo997 said:

May i ask what cause these white nets across the mineral?

Calcite can also be not excluded. You may put a small fragment of the white stuff into vinegar or hydrochloric acid. If it bubbles, its calcium carbonate.

Somewhere on the net I swy also some barite veining in jet, also from Germany. Ah, here it is, left one:
Barite in jet from Germany (link to Mineralienatlas)

 

15 hours ago, Rockwood said:

Maybe it is an achievement to make gemstone from such humble beginnings

Jet is not brittle, its not hard, it polishes very well. Some say, there were mirrors made from this stuff some time ago. I don´t now if its a real story, but jet takes a mirror-like polish very easily and you can see yourself in polished jet very well. Well, reflectance is low, but you can very well see my fingers:

The cracks are filled with white calcite in this Turonian jet from Gams near Hieflau, Styria.

 

15 hours ago, Rockwood said:

Wiki calls it among "the lowest rank of coal"

Typical jet is in the subbituminous field, at the border to bituminous coal, but still with light brown streak.

 

Small variations in rank (water content) and C/H-ratio can make quite some differences in properties and usability of jet as gemstone:

All these are vitrains - coalified wood pieces. Scale bar is 1 cm.

 

Franz Bernhard

Edited November 4, 2022 by FranzBernhard

[Mahnmut]

Jet used to be made into mourning jewelry for obvious reasons.

Low rank refers to lignite in general in terms of energy density for fuel use.

I wonder if that striated structure in your sample is a remnant of the wood structure or due to mechanical stresses, as jet often breaks amorphously like glas.

Cool to have it in the same piece as the ammonite (is it an ammonite?)!

Best Regards,

J

Edited November 4, 2022 by Mahnmut
second thought

[Rockwood]

24 minutes ago, Mahnmut said:

Low rank refers to lignite in general in terms of energy density for fuel use.

Ah HA ! Underachieving as coal. 

[Mahnmut]

You could also say, coming from the humble lignite class, jet is really posh, if useless as a worker...

Talking about the metaphorical social merits of coal, Shungite would be the poor guy from the swamps "working" as a wonder healer under an assumed name...