FMF - Friends of Minerals Forum, discussion and message board

[Hokierocks]

My son & I were playing in the river (Big Gunpowder, Maryland) and he was busting rocks against another. I know its not very a very technical method of science but kids will be kids.
Anyways he found this rust color rock inside one he busted open and asked what it is. I have no clue..... Hoping someone here can lead me in the right direction. Since he is interested I'd love the opportunity to throw in a little education. (He is only 7 so basic is all I need to know).

The rock was white on the outside. The inside has a cottage cheese texture. He is really curious what the red "treasure" is inside the rock. Any help would be great.

Thanks

[Peter Megaw]

Your son is getting a good start...the rock on rock approach has great antiquity and pedigree. Those of us who had to stop taking geologists hammers with us because TSA took them away still resort to the technique in extremis.

This is also pretty much how most geologists start out, so be careful in your encouragement!!

It's a bit difficult to tell from pictures but it looks like your iron oxide blob was originally pyrite. The texture of the surrounding rock looks like coarse marble. Have him try to scratch it with a steel nail. If it scratches easily and leaves some white powder, have him put a drop or two of white vinegar on it...it will probably fizz. This will tell you it is made of calcite. It will also mean he will drip vinegar on every rock he sees for a while. Show him that rocks he can't scratch with a nail won't fizz.

If it doesn't fizz you lose the drama of first time identification of calcite and will have to pursue other physical tests to identify the rock. Some of these are laid out in the introduction to our "what is it section" or any basic mineralogy field guide.

Tell him to keep it up...geology is fun!

[Hokierocks]

Thanks for the response. With great anticipation from the son and a drop of vinegar............ no fizzing. I'll continue the research. Thanks!

I will note that the rock crumbles relatively easily. Possibly sandstone? I always thought sandstone was finer though.

[Bob Carnein]

The "red treasure" inside of the rock may be an oxidized pyrite ("fools gold") crystal. Pyrite easily converts to iron oxide when exposed to weathering. Scrape it lightly against the back of a white porcelain tile; if it leaves a reddish-brown powder (called a streak), it's most likely hematite. If the streak is yellowish brown, it may be goethite. Hematite and goethite are both iron (hydr)oxides that form from the breakdown of pyrite.

[Jeff]

Just a thought. I wonder if this specimen could be a silicified marble. I say this based on a USGS report of the area upstream of the Big Gunpowder River which states:"...much of the area in the vicitity of The Minebank Run watershed (which drains into the the Big Gunpowder River) is bounded by 2 ridges...comprised of metamorphic rocks, namely schists and quartzites. The valley is underlain by marble that is mostly covered
by colluvium and alluvium, with the exception of some parts of the stream channel where the marble is exposed." If it were a marble, it might not react easily to vineger and some scratching of the specimen to generate a powder would likely be needed to notice any fizz from vineger. Further, it would not be unusual for a marble to contain pyrite.
And, yes, many of us who ended up being geologists or in the mining industry started in much the same way as your son....collecting rocks and breaking them open. It is a great profession.

[Hokierocks]

Yes, we were only a few hundred yards away from where minebank run dumps into the gunpowder. My son lost interest now but I'm the one who is more curious. I think it has to be marble. Is this worth keeping in a shoebox for him/me or is it fairly common?

Does anyone know of anything else to keep an eye out for on our next trip? I was telling him about petrified wood a few minutes ago and he thought that was the coolest thing that wood could become rock. Is it hard to find? I've never tried to find it in nature. Might be fun to go on a hunt with him next time we are at the river. (I think I would have fun too!)

Thanks for the help.

[Matt_Zukowski]

One thing that may be good to do is to find a geology club in your area. They will know the local places to find cool rocks, including rocks with crystals growing inside that might be impressive to your son. They may also sponsor field trips to places where one is likely to find more impressive looking specimens.

[Bob Morgan]

I recommend the Baltimore Mineral Society. There are members who know lots of localities among the old mining sites in and around the area. You are lucky! 'So much open and available to explore around there.

[SteveB]

I would keep that specimen, its interior is interesting, I’ve never seen that cottage cheese texture before and when you see specimens in books they are typically high grade examples rather than the lesser grade you actually find in nature. This can make it difficult to identify what you find. I’ve never seen a book which shows well, examples of rocks and minerals in various stages they can typically be found instead of only showing examples that only live in museums. If you visit the Mindat website you can see tons of photos for every rock/mineral from the general public so you can get a better idea of the range of visual appearance possible.

Petrified wood is common and easy to find, but like all minerals it still depends on location. All my personal finds have been on the side of the road near where I lived at the time. You can go exploring especially where roads on the outskirts of town go through hilly areas as the hills are typically cut into when the road was built through the area. Its a great place to see layers and folds in the ground and you can find interesting things that tell the story of how the ground was formed. For example most layers are sedimentary types which can contain fossils or gemstones. If you find a vein of quartz and follow it you may encounter crystals or darker veins in the quartz where the molten quartz brought up metals. So you can find tetrahedrite which may bear silver and possibly even gold. You found marble, I would suggest looking for rock outcrops containing limestone and marble and if you take notes you could follow the outcrops across the landscape and find changes, like quality or quantity and you may find marbles which contain fossils too. Following the surface signs is a great way to learn to read the landscape and find likely spots for interesting specimens. No need to dig or damage what’s there. Rivers can yield interesting smoothed examples but remember they are random and not typically formed where you find them, they get dug out of the banks or fall upstream to end up in the water where they are tumbled and smoothed. So following the water back upstream should lead you to interesting booutcrops. Unfortunately vegetation covers so much of the surface and that can hinder many finds. After storms fallen trees, and gully wash can expose considerable amounts of ground which are fun to explore and can contain great specimens that had been protected by the surrounding earth.

Always be mindful of private property and parklands and restrain from destroying needlessly, there is plenty to see, touch and collect that has already been naturally separated from host rock. Something your son and you can enjoy together outdoors would be geocaching which is like treasure hunting with GPS. It involves people hiding a plastic container of random trinkets for swapping in an out of the way spot. This means the trek to find a cache often takes you through areas of geological interest so you can combine the two activities. Also great if you enjoy photography and wildlife spotting. I highly recommend you look into geocaching. Its fun, good exercise, often educational, and highly addictive with caches everywhere around the globe, so when you travel somewhere there are caches to find. The swapping ethos is great for helping children to not be greedy. Some caches are simply a log to sign, others are huge containers full of books, some are puzzles taking you to many locations, others are themed or of historic significance. Its a great side hobby that complements the exploration of rock hounds very well and neither hobbies are age or gender specific so give them a try for yourself.