I can find no forum like this in US so I am hoping you can help a girl in New Mexico ID some very interesting rocks that I have found. I've always been something of a rock nut but have never discovered anything like these rocks in 50+ years. If your answer is yes, I can send photos. If no, no harm, no foul. Thank you!
There's a good chance we can help you.
Please post photos.
Also, please give us any of this info if you can:
- whether loose or in situ
- whether solitary or just an example from a much larger expanse
- scale (perhaps in the photo, but otherwise some indication of size)
- any tests you have done, eg. with a magnet (to test if iron/nickel rich) / with steel (to test if magnetic) / streak (colour can be indicative)
- this may seem strange, but have you picked it up and shaken it next to your ear? (There is an unusual mineral formation called beekite that often has bean-like pieces containing loose lumps inside;http://www.thefossilforum.com/index.php?app=core&module=attach§ion=attach&attach_rel_module=post&attach_id=148580. It can have various colours, including red.)
Thanks for your reply. Here is what I know:
- location - Central New Mexico, USA. Located in an area once covered, millions of years ago, by a large inland sea. Three inactive volcanoes west of location; Rocky Mountain range east of location. Current conditions - high desert, low annual precipitation, no running water (streams,rivers) within 10 miles of find.
- whether loose or in situ - Found in situ (dug them up myself) at varying depths of 1-15 cm
- whether solitary or just an example from a much larger expanse - All examples found in a narrow strip about .61 meters wide; length of deposit unknown
- scale (perhaps in the photo, but otherwise some indication of size) - examples are .63 cm to 2.54 cm in length. Most are jelly bean shaped and with red markings in what may be quartzite; other smaller samples are irregularly shaped; some are darker reds amalgamated with a gray rock. Some of the samples are also rough & pitted but the majority are smooth and oval, as if tumbled.
- any tests you have done, eg. with a magnet (to test if iron/nickel rich) / with steel (to test if magnetic) / streak (colour can be indicative) - They are not magnetic; they do not float. I even licked them; they taste like a rock. They are not inordinately heavy or light. They all definitely have that red distincive coloring in them.
- this may seem strange, but have you picked it up and shaken it next to your ear? (There is an unusual mineral formation called beekite that often has bean-like pieces containing loose lumps inside - I did shake them. No sound.
I certainly do appreciate you taking the time to help solve my mystery. Let me know if you have any other questions. Thank you!
Good info, thanks Jeanne.
I should have been a bit more specific in asking about being in situ or not.
I'm guessing that by your saying in situ, you mean in recent sediment (not in solid rock, which I intended).
They are pebbles of red quartzite.
There is a widespread red-pink quartzite called the Sioux quartzite, which extends into north central New Mexico - see http://en.wikipedia.org/wiki/Sioux_Quartzite.
There is also a brick-red quartzite conglomerate that comprises much of the El Rito Formation
And other red beds.
You'd have to look at a geological map of the area to determine the likely source rock.
Whatever rock comprised the source of the material, your pebbles are probably not due to the synsedimentary processes that laid it down. They were probably formed much more recently (few hundred to few million years), as those sedimentary rocks were eroded, and the pieces tumbled and polished in a stream bed or on a lake shore. The linear nature of the occurrence you describe hints at a stream bed, but could be either.
I say 'probably' because there is a chance your pebbles were formed much longer ago, and redeposited to form a conglomerate (as occurs in the El rito Formation, above). Recent erosion has a propensity to pick-out such old pebbles from a congolmerate, and hence it can be difficult to say at which stage the pebbles were formed (sometimes there are clues, such as preferential pressure solution pebble-to-pebble, but there is none of that in your specimens).