Ask a Geologist Common Q&A
I found these rocks with what appears to be sea shell fossils while digging in my yard. They were at a depth of two feet. Are they rare and what should I do with them?
thanks Glen.
AZGS Answer
Glenn, They look like stream-rounded fossil-bearing (fossiliferous) limestones. These sorts of rocks are pretty common in the western and Midwest U.S. and elsewhere in the world. They are attractive but I don't believe they have any economic value.
Mike
The ground outside my home has a number of small depressions. I've filled several with dirt and they continue to recur.
AZGS Answer
We have had a number of calls and e-mail about small depressions (measured in inches or tens of inches) in Phoenix, Tucson and elsewhere in Arizona.
For the most part these are probably minor problems associated with local 'collapsing soils' where the soil is not well compacted. Small voids may exist in the shallow subsurface and over time the voids collapse resulting in localized collapse at the surface. This can happen in former agricultural lands as well.
Two things to do:
1) See our Down-To-Earth booklet: A Home Buyer's Guide to Geologic Hazards in Arizona pages 11 – 15 on problem soils.
2) Contact your local Natural Resources Conservation Service office - a federal agency that specializes in soils.
> In Phoenix: 230 N. First Avenue, Suite 509 ( (602) 280-8808 )
> In Tucson: NRCS - 2000 E Allen Rd, Tucson, AZ 85719 ( 520.670.6602 )
Good luck with it.
Mike
What type of minerals are available to the public for collecting and where do I find any near Payson Az? Denise
AZGS Answer
Hi Denise,
On Federal lands, BLM, US Forest Service, you can collect any and all minerals. There are some limitation on collecting fossils and you would need to contact BLM about that.
Arizona State Trust Lands are off limits to collecting unless you have a permit.
Payson is surrounded by the Tonto National Forest, so there are plenty of places to hunt for minerals. For details of land management status, see AZ State Land Dept http://gis.azland.gov/webapps/parcel/ . Be sure to turn on the Land Ownership layer.
The interactive Geologic Map of Arizona can provide basic information on the rocks and minerals in the Payson area; I captured a snippet of the map below. http://data.azgs.az.gov/geologic-map-of-arizona/#
Hi! My name is Nicholas. I am currently going to Middle School in Glendale AZ. I am doing a powerpoint on geologists and I had a couple of questions that I would like to be answered.
1. What age did you become a geologist?
2. What made you interested in geology?
3. What is your favorite part about geology?
4. What has been your favorite discovery (if any?) 5. What is your favorite mineral?
AZGS Answer
Hi Nicholas,
Happy to help:
1. What age did you become a geologist? 27 years old
2. What made you interested in geology? I really enjoyed the physical processes, such as volcanism, that impact and sculpt the Earth's surface.
3. What is your favorite part about geology? Physical volcanology and talking to people about geologic features and processes.
4. What has been your favorite discovery (if any?) Some work I did published on the frequency of cinder cone emplacement in Arizona's San Francisco volcanic field.
5. What is your favorite mineral? That a tough call. I like hornblende, plagioclase (anorthoclase) and tourmaline.
I found a rock in Tucson Arizona that looks like it is encased in Quartz? Have you heard of this before? thanks! Lisa
AZGS Answer
Lisa, It certainly appears to be crystalline rose quartz attached to a volcanic basalt or andesite cobble. Secondary minerals, like the rose quartz, form as silica-rich, oversaturated fluids, move through existing fractures in rocks. When conditions are right (temperature, pressure, and fluid chemistry) the oversaturated silica plates out onto the surrounding rock.
This is a great example of that. Thanks for sharing the image.
Mike
I can't seem to find any information about historic clay mining around the Phoenix area. I would love to read about it. Any suggestions on books or online information? Thank you for any help you can give me! Thanks, Vanessa
AZGS Answer
Vanessa,
Great question and not an easy one. Most historic mining reports focus on copper, gold, silver ... Clay goes largely overlooked. Here are some online resources that include discussions on clays in AZ.
Industrial Minerals (includes statewide map showing clay mining? distribution in AZ - p 12-13) http://repository.azgs.az.gov/uri_gin/azgs/dlio/1600
Geology & Mineral Resources of AZ (part v, p. 324) http://repository.azgs.az.gov/sites/default/files/dlio/files/nid1005/bulletin-180_part5.pdf
There is said to an excellent source of pottery clay near Kingman, AZ. You might try the local Chamber of Commerce there.
If you are interested in soils, which frequently include clays, the University of Arizona Press 'Arizona Soils' is online at:
http://www.library.arizona.edu/exhibits/swetc/azso/
For a report on Horseshoe Dam clay in Maricopa County: http://docs.azgs.az.gov/OnlineAccessMineFiles/G-L/HorseshoeDamClayMarico...
I hope this helps.
Mike
I recently found a chunk of rock while walking around and I can't figure out what it is. Would you mind helping out with the identification of it please? It kind of looks like pumice but it greyish in color with goldish or copper color metallic flakes and white and yellow banding on part of it. Carl
AZGS Answer
Hi Carl, Thanks for the pictures, one of which is shown here.
The whitish to opaline material looks like a secondary silica gel that commonly occurs in hydrothermal environments where silica (SiO2) is saturated in the liquid phase, causing it to precipitate on a host rock. Take the blade of a pocket knife and drag it across the white material. If the knife blade leaves a metal gray streak it is softer than the white material. That would be characteristic of a silica gel, which has a hardness of seven, like’s its crystalline relative quartz. Unfortunately, magnifying the images just cause them to blur. I’m hard put to describe the rock minerals. I do suspect that this rock occurred in an area of highly altered rock, perhaps associated with copper ore. I can barely make out platy looking minerals. If they are really platy, again try the knife blade, if they are soft and flaky they are probably a form of mica – muscovite (silvery) or (biotite); there are other micas as well. If instead of being platy they are rectangular prisms, they are probably altered pyrite. I hope this helps. Mike
I recently found a chunk of rock while walking around and I can't figure out what it is. Would you mind helping out with the identification of it please? It kind of looks like pumice but it greyish in color with goldish or copper color metallic flakes and white and yellow banding on part of it. Carl
AZGS Answer
Hi Carl, Thanks for the pictures, one of which is shown here.
The whitish to opaline material looks like a secondary silica gel that commonly occurs in hydrothermal environments where silica (SiO2) is saturated in the liquid phase, causing it to precipitate on a host rock. Take the blade of a pocket knife and drag it across the white material. If the knife blade leaves a metal gray streak it is softer than the white material. That would be characteristic of a silica gel, which has a hardness of seven, like’s its crystalline relative quartz.
Unfortunately, magnifying the images just cause them to blur. I’m hard put to describe the rock minerals. I do suspect that this rock occurred in an area of highly altered rock, perhaps associated with copper ore.
I can barely make out platy looking minerals. If they are really platy, again try the knife blade, if they are soft and flaky they are probably a form of mica – muscovite (silvery) or (biotite); there are other micas as well. If instead of being platy they are rectangular prisms, they are probably altered pyrite.
I hope this helps.
Mike
Hello I have been trying to figure out what this rock i found is or what mineral it is displaying ever since it was found up in Peeples valley. I have pics but i dont see anywhere to post them. its a creme/beige color with different layers showing and all over it are these perfect squares with smaller and smaller squares inside each one all the way down to basically a dot. the outter most square is probably 3/8'''-1/2'' in size and u can see partial squares coming out from the lower layers partially covered by the upper layers. i hope that is a good enough explanation, if not i can send pics to you. thanks for any help you can provide.
AZGS Answer
Jerry, great pictures. It appears to be an igneous rock containing crystals of pyrite, iron sulfide (FeS2). The box-within-box appearance suggests that these are zoned pyrites. I wish I could be more certain of my analysis, but this is the best I can do with pictures. The thin, nearly parallel bands of iron staining are referred to as Liesegang banding”, representing precipitation lines of iron-rich minerals (e.g., hematite, limonite, goethite, etc.).
Cool rock.
Mike
, 
Hello, I live in The Valley in California and in my basement the ground is covered with gold flakes the dirt is everywhere and even inside the chimney there's like gold sandstone flakes in it. How can I tell if it's real gold or not or if I'm just digging up fools gold because the ground is got alot of gold in it. Jessica
AZGS Answer
Jessica,
A more likely candidate is biotite. Biotite is a common platy mineral that when oxidized takes on a gold sheen. Try scratching one gently with your fingernail. Biotite is very soft and platy. You should have no trouble scratching or leaving an indentation.
If you want to take some high quality pics and send them to me, I'll eyeball them.
Mike