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.