I was like 10 waiting for my dad to get off work. He was a surveyor and brought this blue rock thing with him for me when he got off. He said they were surveying and his friend took a pickax to a rock and this broke off. There was of course some dust and shattered pieces with it to (like 12 years ago when i got it). I don't know anything about rocks, gems, crystals, and all of that, but everyone I ask that does can't tell me for sure what it is. Only good guesses. In my own research it looks like a blue opal, blue granite, or blue agate. But they have only a little bit of similarities with it, not exactly the same, not even close enough to say for sure.

It's heavy and almost the size of my head. It was found on a construction job site in Seattle.

I just wanna know what it is for sure since it's been such a mystery. Some people said man-made but I was there on the job site. From what I remember they asked if I wanted more because it was the size of a car down there.

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closed as off-topic by Jan Doggen, uhoh, Erik, Fred, Gimelist Aug 28 at 10:13

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  • "Questions about rock identification requests are off-topic. For more information, see the announcement on meta." – Jan Doggen, uhoh, Erik, Fred, Gimelist
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    $\begingroup$ Looks like some sort of glass slag to me. $\endgroup$ – MaxW May 11 '18 at 8:01

I am pretty sure that it is bulk or recycled glass. It might have been a discarded or lost piece left from previous users of the land. Glass rocks have also been used for landscaping which might fit with the discovery location. I haven't seen any natural rock with such blue and uniform coloration. At various rock stores you can find similar material, it is often called "Slag Glass". I encountered material very similar to it in Quartzite Arizona.
Slag Glass

Slag glass for sale

Slag Glass on eBay


Thats a rare colored type of basaltic glass or volcanic obsidian. Its blasted out of volcanic erruptions in broken blobs. Volcanic glass is another name for it. Its a really nice piece, i know that blue rough obsidian comes from montana and a few other places.

  • 3
    $\begingroup$ No, this is not obsidian. This is man made glass. $\endgroup$ – Gimelist May 12 '18 at 2:47
  • $\begingroup$ We cant be for sure if this is fake or not without taking it to lab and test it. I have seen the fake chinese glass and its clear and clean of swirling. I have seen authentic blue obsidian which is opaque with some swirling albiet a different shade of blue. I wont claim to know absolutly since volcanic glass tends to be different depending on its source and i have never seen every type that nature has produced. $\endgroup$ – Armondo Villaescuza May 13 '18 at 3:20
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    $\begingroup$ No. This is not obsidian. I don't know about "fake" or not, because if something's fake it was meant to imitate something. This could just be a piece of blue glass. The while swirls do not form in natural obsidians. This bright blue requires small amounts of cobalt (or copper) which also normally occur with iron. Even 1% of iron would give it a very dark colour. According to OP, this was found from a huge block in a construction site. Had it been real, it would be a mining site, not a construction site. Anyway, It's glass. Not obsidian. $\endgroup$ – Gimelist May 13 '18 at 4:55

It could be a Larimar stone. You can check online for pictures and see if they match your rock.

  • 1
    $\begingroup$ Please justify your answer. $\endgroup$ – arkaia May 14 '18 at 16:57
  • $\begingroup$ No. Larimar is mineral which commonly crystallises in a rounded or boytroidal form. $\endgroup$ – Gimelist May 14 '18 at 22:39
  • $\begingroup$ I have a Larimar, and it kind of looks the same. But I'm no geologist and you guys should know better. $\endgroup$ – Sabrina Tariq May 15 '18 at 6:12

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