Ask a Geologist Common Q&A
I have a question about a crystal please write back so I can send the video I need you to tell me what type of crystal this is. Jeremy
Ed. note: see picture captured from video below.
Jeremy, I suspect it is a fragment of petrified wood that hosts some larger, granular crystallization. I can’t be sure based on the video, but I think the coarser materials are crystals of quartz. (Quartz or silica is frequently involved in the petrification process.)
Thanks for the question. MC
Hello, I have heard that Buffalo River chert, when freshly broke is a reddish color, but after being in the ground for a thousand years, it will patina to a pinkish color? Your thoughts? Thanks , Jeff
Hi Jeff, Chert is a really fine-grained sedimentary rock made up of microcrystalline silica. It is very hard, brittle, chemically stable. The color of chert varies greatly. Red coloration is the result of small amounts of iron that finds its way into the crystal lattice during formation.
I don't think that sitting in the ground for 1000s or even million of years will have much impact on the interior makeup or color of chert. It's chemically inert. You might see some discoloration on the outer perimeter, probably due to post deposition oxidation of the host rock.
I hope this helps and thanks for a great question.
Hi, I'm looking at purchasing a home in Chandler, Arizona, and I would like to avoid the problems that accompany expansive soils. Am I safe in Chandler. Sean
Hi Sean. Expansive soils are clay-rich soils that expand when wet and shrink when they dry out. They are frequently called shrink-swell soils and they are common in many places in the U.S. including Arizona.
Investigating and characterizing soils is outside the scope of the mission of the Arizona Geological Survey. But we do know where you can go for soil information, the Natural Resources Conservation Service (NRCS) of the U.S. Dept of Agriculture. The NRCS has an office in Phoenix and can be reached at 602-280-8826. Their web services are located here: https://www.nrcs.usda.gov/wps/portal/nrcs/surveylist/soils/survey/state/?stateId=AZ
NRCS provides a marvelous online soil mapping tool, Web Soil Survey .
For more on problem soils, see our Down-To-Earth booklet: A Home Buyer's Guide to Geologic Hazards in Arizona; see pages 11 - 15.
Hello. I am exploring the availability of online water well log databases for the USGS. I discovered AZGS was involved in compiling several state well log databases that ended up being distributed on data.gov. Unfortunately none of the state databases could be downloaded from their site. I either experienced a "can't find the web page" message, or the web page said the "link to the file is broken". Could you ask around and determine if there a way for the USGS to obtain these datasets?
I believe that we can help. Here are well URLS for well data - Water & Oil & Gas
- McGarvin, T.G. and Trapp, R.A., 1994, AZWELL: A digital database of the Arizona Geological Survey Well-Cuttings Repository. ) Arizona Geological Survey Digital Information-2, 6-p report, 1 ASCII file.
- Scurlock, J.R., 1973, Arizona Well Information: Supplement 1. Arizona Bureau of Mines, Oil and Gas (OG)-26, 30 p
- Arizona Well Information - 1972 4 parts (pdf documents)
- Interactive Arizona oil and gas well viewer (w geophysical logs and downloadable data). http://welldata.azogcc.az.gov/
You might chat with the folks at the Arizona Dept. of Water Resources. They should have quite a bit more data in easily consumed digital form.
What happened to the Department of Mines & Minerals files & Nyal Niemuth? Doug
Doug, good questions. The former died while the latter lives.
ADMMR went belly up in 2010-2011. The Brewer Admin shuttered the museum and handed off the mineral collection to the Arizona Historical Society. In 2016, the mineral collection and old museum (Polly Rosenbaum Building) were transferred to the Arizona Geological Survey. A year later, the collection and museum were transferred once again to Research, Discovery & Innovation team at the Univ of Arizona. Both collection and museum reside there today.
Nyal is alive and well and semi-retired in Phoenix, Arizona. After the demise of ADMMR, Nyal hired on with us at AZGS through June 2016, when he retire after 30+ years in service to the state of Arizona. In July 2016, AZGS was taken out of service as a state agency and transferred to the Univ of Arizona. We reside there today.
There you have it in a nutshell.
I recently went hiking in the Aravaipa area and saw several reddish-brown rocks with white "scratch" marks on them. The rocks were of various sizes ranging from palm-sized to the size of a loaf of bread. The entire surface of the rock was covered in small holes similar to pumice but with only a fraction of the holes. The "scratches" are in random directions and cover the entire rock. They are about 1/4 to 1/2 inch long. I am curious as to what would cause the white marks--they do not seem to be a different mineral within the rock. I have a picture I can send in if you would like it. Ric
This is a volcanic rock, probably an andesite or dacite. The white linear features are mineral crystals of the feldspar mineral family – the latter is a guess but I’m pretty confident. The small half-sphere indentations appear to be vesicles. They occur when gas – H20 mostly – escapes from the cooling lava.
This rock has porphyritic texture – larger mineral grains in a groundmass of finer grained minerals.
Thanks for sharing the image.
Good day, I have a question regarding Pleistocene to Holocene river deposits. Commonly along the Agua Fria and the Salt River channels, and about 20-50 ft below the surface elevation, exists cross-bedded, poorly sorted cobbles and pebbles with a distinct even black coating. The black coating is not a weathering rind since it does not penetrate the surface. It also seems to coat the entire cobble with no preference to orientation. I have a few interpretations such as preserved algae (but if true, I would expect a preferred orientation of the coating to be on the "top" of the cobble), desert varnish during a dried abandoned river bed event (but again - orientation is a problem), ground water contamination (but I might expect more of a rind in the cobbles and that elevation should be more consistently black), or an organic coating from decayed fauna or flora? It seems that the latter of the options is most likely.
Since I've noticed this at a distinct depth below surface and according to this source; http://azgs.az.gov/arizona_geology/summer09/article_sanpedro.html
"...the presence of orange or black coated pebbles and cobbles on Pleistocene-age surfaces is equally diagnostic". Are there any research papers available that further explain the diagenesis of black-coated cobbles of Pliocene to Holocene age?
Let me know if you'd like to see some pictures and I'll send them over. Thanks, Cameron
Cameron, My guess is that the black gravel coatings are mainly manganese and iron oxide concentrations. These compounds give desert varnish its brown or black color, but can also be deposited by groundwater. There are some nice examples in our Dome Rock Mtns SW quadrangle map (Jon Spencer and I led an AGS fieldtrip to this area in 11/15), where manganese and iron coatings exist on basal Bouse carbonate but also in gravel layers in old Colorado River deposits (Bullhead Alluvium) and tributary gravel deposits.
Contributed by Phil Pearthree, Arizona State Geologist; Photos by Brian Gootee, AZGS Research Scientist
Good day; What is the chance of the North Phoenix area (xxxx Rose Garden) and xxxx Avenue in Chandler being affected simultaneously by flooding? Martin
When I searched for xxxx Rose Garden., the Maricopa Floodplain Viewer brought me to Rose Garden Lane, north of the intersection of 101 and I17. If that is correct, that address is not included in the 100 year floodplain. Thus, unlikely to flood.
The floodplain viewer could not find xxxx Ave., Chandler. Have a look for yourself. You can avail yourself of the Maricopa County Floodplain Viewer at
Good luck with it.
My name is Ivan and I am in the fourth grade and I was watching a video of the Hawaii volcano eruption. And I was wondering how lava gets to the surface of the earth through the spout of the volcano and why magma is at the center of the earth and why is it hot? My tutor is typing this for me.
Thank you for your time.
Ivan and Ms. Andrea
Hi Ivan, We know a lot about how magma - molten rock, forms - and we know a lot about volcanic eruption processes. But what we know is greatly outweighed by what we don't know.
For example, we know that magma's originate in the upper part of the Earth's mantle, not in the Earth's core. You are correct, the outer portion of the Earth's core is indeed liquid. But that molten material does not erupt onto Earth's surface.
We don't really understand the physics of how magma rises through the upper mantle and lower crust. The pressures are so great it's difficult to understand how vertical conduits capable of carrying tremendous volumes can open and remain open.
But it happens, so there must be a physical explanation, we simply have not discovered it yet.
So what causes rocks in the upper mantle to melt? A key factor is the concentration of radioactive elements. As those elements radioactively decay they produce heat. Couple that with heat resulting from great pressure and residual heat from the Earth's formation 4.5 billion years ago, add a little water - at subduction zones - and wa-la, magma. The density of magma is less than the surrounding rock - making it buoyant and capable of rising into the crust.
Have a look at this cross section of Earth showing the crust, mantle and outer and inner core.
Good luck with your studies,
Is there a single digital database of mine locations, commodities, production, and status for Arizona? Jason
Hello Jason, There does exist a large database for mines in Arizona. It's hosted by the US Geological Survey as part of their Mineral Resources Data System. MRDS includes data for nearly 13,000 mines in Arizona. And bear in mind, that tens of thousands of undocumented mines - many no more than shallow exploration pits - exist in Arizona.
You can access and download these data from the USGS Mineral Resource Data System.
There are 45 fields in the database, including location - state, county, latitude & longitude - host rock, commodity, gangue minerals, ore geometry (if known) and more.
Another important source of mine data for Arizona mines is the AZGS Mining Data website. It comprises materials - reports, correspondence, assay results, drilling data, mine maps and geologic maps and 1000s of vintage photos of mines.
Good luck with your research.