Black glasslike "rock" with iron nodules from the beach in Florida

[PetesPockets55]

Evening everyone. Let me start by saying geology is not my strong point by any stretch of the imagination.

I found the following "rock" sticking out of the face of a beach dune after a strong northerly blow this weekend. It had quite a bit of sandlike material adhered to it when I found it but there were enough dark spots to get my interest. I have only rinsed it enough to get the loose sand and debris off.
The curving triangle is about 6 x 5.25 x 4.5 cm and about 2.5 cm thick and weighs 103.3 grams (2.25"x2"x1.75"x 1"thick +-3.8 oz)
There seems to be two layers. A black glasslike layer and an underlayer of hardened sandy material. Imbedded in the sandy material appears to be iron "nodules" or bits (which may only be some kind of contamination?).
I would love to get an idea of what this material is since this area of Florida (South Central East coast) doesn't really have traditional "rocks" as far as I know. Just coquina, limestone and such.

Anyway, enough yacking. Let me know if this might be obsidian or something else. If so, any ideas on how it might have gotten to the area? Spanish ballast piles, native American trade, etc.

Should I leave as is or try to remove more of the sandlike substance on the surface with a quick and diluted acid wash?

Thanks for any insight and info. PP55

 

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[DDancer]

I'd try the acid on the glassy part and leave the sandstone dry for contrast. Difficult to say if its obsidian or just some slag melt on solidified sand.

 

[PetesPockets55]

Thanks DDancer. Does slag melt resemble glass? I always thought slag was dull and full of bubbles. I'll include images once I've acid washed it.

This one has me flummoxed because of how unique it is (to me anyway). I have a couple of ideas on it's origin but would love to hear from others with more experience.
1)A past beach renourishment where the sand is brought in from pits further inland?
2)Ballast stone?
3)Trade item from Native Americans?
4)Modern debris?

The iron nodules seem odd since I would have expected them to dissolve away in the harsh salt environment.

 

[DDancer]

Slag glass comes in all shapes and varieties, even obsidian can have bubbles as it to is glass. Have to clean it up for a better idea. The iron could be concretions or pyrites both of which can occur in native sandstones. As to your other questions anyone of them could be valid. Just dont know but I'd rule out it being a trade item as the material would have been much more clean.