This is my first time posting in a forum of any sort, so I apologize if this question should have been directed to a specific topic area. I found this beautiful rock while I was on a beach near my school, and I found a handful more that were like it. I’m not really sure what it is, though— I’ve never seen anything like it before. I’d take it to a geology professor if my school had such a department. I’m hoping I can find some help here!

This is my best description, although I have no knowledge of geological vocabulary:

The rock is roughly an oval, about two inches across. Its main color looks black, but there’s lots of reflective shiny bits all around it. In the light of a flashlight, the reflective bits look almost bronze. In the sun, however, it reflects all sorts of beautiful colors like red, blue, green and yellow. I don’t have a way to accurately weigh it, but it’s surprisingly light for its size. I would’ve expected it to feel heavier.

Here’s the “front” of it: enter image description here

Here’s another angle: enter image description here

Here’s the “back” of it: enter image description here

Thank you for taking the time to look at my rock and for any help you may provide!


Here’s another picture with some natural light; hopefully you can see some of the colors I was describing. enter image description here

Edit 2:

Here is the extra info you asked for (thank you for pointing me in the right direction, by the way). For some reason, I’m having a hard time posting extra photos (the files are too large all of a sudden), so I’ll just have to tell you what my results were.

Hardness: the first item on the list provided that made a scratch was the knife, though I had to use a little bit of force to make sure it wasn’t going to slip off and cut my finger (the rock is fairly smooth). The knife, according to the list, has a hardness of 5.5

Length/Width: “longer” side measured between 5 and 6 cm. “Shorter” side measured approximately 4 cm at its widest point.

Weight: ~45g

Volume: ~37.5mL

Location: 41.4875N 71.0383W. It was on a beach, just lying in the sand a decent way away from the shore. There were lots of others like it near by, but all smaller and less shiny. I didn’t have to dig for it.

Description: I noticed when I was measuring the volume that when I put it in water, some bubbles came out of it. I’m not sure if that means it’s porous, as it doesn’t look like it has holes. Rather, it has lots of smooth flat parts that reflect light, which may look like holes from afar, but appear flat and shiny upon closer inspection. It’s fairly smooth, probably from tumbling around in the ocean. Like I said before, it feels lighter than it looks when I pick it up. It doesn’t seem to be very fragile.

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    $\begingroup$ Looks like a weathered piece of coal, especially given its weight. If you look at the following site and fill in the missing data in your question myself or other people are better able to give you a definitive answer to your question. earthscience.meta.stackexchange.com/questions/124/… $\endgroup$ – Friddy Jan 7 at 22:30
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    $\begingroup$ Got it, I will add this info tomorrow. Thank you! $\endgroup$ – just.wondering Jan 8 at 1:41
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    $\begingroup$ I think I know what is the blue, but we do not answer before linking the guide. If you have time please put a picture with a rule for scale. Give precise location (if it is not a trouble exact coordinates). And if you weigth it and surely if you do the test to give us aproximate volume (then we will have density), me or better a better geologist will answer you. earthscience.meta.stackexchange.com/q/1663/12525 $\endgroup$ – Universal_learner Jan 8 at 4:11
  • $\begingroup$ Thank you for providing those links! I’ve edited the post to the best of my ability. Unfortunately it’s giving me a hard time adding pictures, but I have listed out the information. $\endgroup$ – just.wondering Jan 9 at 16:13
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    $\begingroup$ @Friddy if you still think this is coal, you should post an answer. $\endgroup$ – Spencer Jan 17 at 17:09

It is asphalt AKA a tar ball

wave tossed asphalt and petrochemicals are fairly common, especially on the east coast of the US. I have a few in my own collection just for the educational aspect.

The light weight and conchoidal fracture is a dead giveaway. stick a hot needle in it and the smell will confirm. Wave tossed building tar or asphalt ends up in the ocean all the time. It can also be creased by old oil spills. It could even be natural, natural oil seeps do exist.

You can find rocks made of tiles, old bricks, even plastic on today's beaches. The are called anthropogenic minerals or anthropogenic rocks. If your ever bored look up "sea bricks"

enter image description here


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