What is this? Rock/Geoformation

[Arich1819]

Hey I’m new to the website but after skimming through forums I think that I came to the right place.

So recently my grandpa passed away, and when we were cleaning out his basement I came across a big rock wrapped in a towel for protection. It’s about 2 ft x 1 ft, and weighs about 65-75 lbs.

I was curious about the formation on it and asked my aunt if I could keep it. She agreed and told me that when my grandpa was stationed at Camp Pendleton he came across the rock and kept it. That was about 65 years ago now.

Any help on identifying it would be much appreciated!

 

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[Eu_citzen]

That's a tricky one. Use the backside of the specimen and see if a knife will scratch it. Maybe someone more familiar with the area will join in.

 

[stdenis_jd]

That's a tricky one. Use the backside of the specimen and see if a knife will scratch it. Maybe someone more familiar with the area will join in.

also try an acid test - if you have any pool acid (muriatic or Hydrochloric) put just a drop on it and see if it fizzes, then neutralize it with water (rinse). If you don't have that strong of an acid, try white vinegar - the reaction will take usually 30 seconds to two minutes to see bubbles rising from the surface.

This is basically to rule in or out calcium/calcium carbonates like limestone & dolomite

 

[Arich1819]

Okay sweet! I’ll give both of these a try later today and let you guys know what happens. I’m kinda new to all of this so thanks for the tips guys!

 

[bologna321]

looks like cave popcorn to me, aka calcite

 

[Arich1819]

So after scratching with a knife, it came off very easy in little grains of sand so I am guessing limestone?
Also, I don’t have either of those acids, so I used vinegar and like you said, it began to fizz ever so slightly. I noticed that the bubbles were coming from a few certain spots in particular if that means anything.

I ended up just googling “cave popcorn” and I think your right. It looks almost identical to several that I saw. So does that mean that this piece was removed from a cave, or is there any way that this type of formation would occur anywhere outside of a cave?

 

[bologna321]

Any void could grow it really that had ground water entering it in limestone.

He may have taken it from a cave or it somehow ended up outside.

 

[Arich1819]

Sweet, no further questions. I think we got it solved! Thanks guys