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Rocks are very dense and when split in half contain what appears to be melted metal of some sort. I took a few close-ups. A lady I know has these in her rock garden, she found the rock which used to be in one big chunk about 30 years ago in West Texas. It took two grown men to lift it.

If you have any questions, I will do my best to answer them.

More images can be seen here.

Unknown rock

Unknown rock

Unknown rock

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closed as off-topic by user12525, Erik, Fred, Gimelist, daniel.neumann Aug 28 at 11:37

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  • $\begingroup$ Have you got a strong magnet? See if you can find any magnetic minerals. Next, take a nail and scratch the metallic minerals; get a clear close up photo with a coin or pencil for scale and post it please $\endgroup$ – Shawn Dec 20 '16 at 10:44
  • $\begingroup$ viciouz, are you saying all of your samples came from the lady's original find in west Texas, or that she has a version she describes that way but you have a different version? $\endgroup$ – JeopardyTempest Mar 11 '17 at 13:49
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The black core looks like a poor quality 'snowflake' obsidian. Some of the paler rock appears to be a thick hydration or de-vitrification rim, whilst the more granular samples are clearly a crystallised rock of the same composition as the obsidian. One would need to get a thin section of the rock under a polarizing microscope to say much about the composition, but my guess is that it is an acidic (rhyolitic), or possibly more intermediate, volcanic rock. This would tie-in with the geology of parts of West Texas. I'm pretty sure it is not 'melted metal'. Rather, it started off as a viscous extruded magma flow with a complex cooling history - the fast cooled rock is the obsidian whilst the more granular rock facies will have cooled more slowly, allowing the individual crystals to grow larger. I suspect the white flecks, or 'snowflakes are a high temperature polymorph of quartz, probably cristobalite.

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  • $\begingroup$ Looks like those clasts could show sedimentary grading though. Pictures aren't great (and no scale) but I would say it looks more like a volcanoclastic. You say obsidian, but I don't see any conchoidal fractures... $\endgroup$ – Shawn Dec 20 '16 at 10:42
  • $\begingroup$ @Shawn could be heavily devitrified obsidian, and then you don't get the conchoidal fractures $\endgroup$ – Gimelist Jan 9 '17 at 20:26
  • $\begingroup$ Obsidian is relatively not dense. The OP mentioned that two men needed to lift the rock, and picture two shows a mineral with potentially metallic lustre. The mineral also seems to have a visible habit (look centre left). West Texas has a few metal mines out west, eg, the Bonanza Mine. These contain molybdenum and galena, which match the poster's description better that obsidian. $\endgroup$ – Shawn Jan 9 '17 at 20:34

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