Assistance with a rock identification (found in the Southwestern US)

In summary, The rock came from southwestern New Mexico and it has a greenish-gray color, with streaks or bands of quartz (white material). The photos were taken with direct sunlight, and the second photo does not show the streaks or bands as well. The rock is from the edge of a magma duct that came to the surface, so it contains more bedrock than magma.
  • #1
C Mac
6
2
Hello,
Thanks for providing a forum where people can share their education/passion and help others. Speaking of helping out, could I please get some feedback on this rock I came across in the southwestern part of the U.S.? I picked it up because it didn't match anything else in the area. It sat around my place and I eventually put a magnet to it and it was magnetic. I also did a scratch test on ceramic and it didn't leave a mark. In my not very scientific way, I thought it was magnetized sandstone. Maybe it's weathered magnetite? Attached are a few photos. Please let me know what you think when you have a moment.
Hopefully you can see the images.

IMG_8153.jpg
IMG_8151.jpg
IMG_8152.jpg
 

Attachments

  • IMG_8153.jpg
    IMG_8153.jpg
    63.6 KB · Views: 796
  • IMG_8151.jpg
    IMG_8151.jpg
    75.1 KB · Views: 841
  • IMG_8152.jpg
    IMG_8152.jpg
    61.5 KB · Views: 824
Last edited by a moderator:
Earth sciences news on Phys.org
  • #3
C Mac said:
Maybe it's weathered magnetite?

I don't think so ... magnetite will weather/corrode to a reddish colour aka rust ( as with most iron minerals)

Many rocks will stick to a magnet because of their iron content, even basaltic lava

1) is it really green in colour or is it the camera/lighting ?
2) the darker areas, do they really look like they are clumps of material in that green/white matrix ?
3) where in the SW be more specific ... state, area in the state ?
4) in that last photo with the white patches, it (well that area) looks much like dacite ( volcanic)
5) the overall appearance looks like a conglomerate of several different rock typesVariations of dacite ...

SuperRocks3b.jpg
Dave
 

Attachments

  • SuperRocks3b.jpg
    SuperRocks3b.jpg
    95.8 KB · Views: 815
  • Like
Likes C Mac
  • #4
Thank you for the replies. The rock came from southwestern New Mexico. I do historical research. While not looking for rocks, I'll pickup odd rocks that don't match the terrain. To answer additional questions, it's a dark gray/greenish. The photos, including the first one in this photo, were taken with direct sunlight since I was trying to pullout the various colors and features. The second photo in this posts shows the rock with no direct light.

Thanks again and please let me know if you have additional questions.

IMG_8044.jpg


IMG_8052.jpg
 

Attachments

  • IMG_8044.jpg
    IMG_8044.jpg
    92.1 KB · Views: 725
  • IMG_8052.jpg
    IMG_8052.jpg
    81.5 KB · Views: 750
  • Like
Likes davenn
  • #5
Could it be maghemite?
 
  • Like
Likes C Mac
  • #6
C Mac said:
Thank you for the replies. The rock came from southwestern New Mexico. I do historical research. While not looking for rocks, I'll pickup odd rocks that don't match the terrain. To answer additional questions, it's a dark gray/greenish. The photos, including the first one in this photo, were taken with direct sunlight since I was trying to pullout the various colors and features. The second photo in this posts shows the rock with no direct light.

thanks for the additional info
Well, New Mexico - Arizona area has a lot of old volcanics so that could explain the dacite
the green stuff with streaks / almost banding of quartz ( white material) through it gives the appearance of gneiss - schist

one gneiss variation ...

diorite-gneiss-ted-kinsman.jpg


The green is usually because of chlorite content.
Gneiss and schist are old metamorphic bedrock rocks. the presence of what looks like those darker lumps of dacite,
hints at the possibility that volcanics came up through the gneiss bedrock and tore bits off resulting in this mix of
two very different rocks.
Because the "gneiss" is more prominent than the darker patches, this hints that the sample was from the edge of the
magma duct that came to the surface through the bedrock... hence more bedrock than magma in the sample

This is my best educated guess without seeing the sample(s) up close for myself. I remember seeing a similar thing
(different rock types) but still volcanic and country rock mix when I was studying the "Dunedin Volcano" ( New Zealand)
back in my university days.
Dave
 

Attachments

  • diorite-gneiss-ted-kinsman.jpg
    diorite-gneiss-ted-kinsman.jpg
    81.4 KB · Views: 706
  • Like
Likes C Mac
  • #7
Vanadium 50 said:
Could it be maghemite?

I had to google that one :wink:
not one I was familiar with
Maghemite - Wikipedia
https://en.wikipedia.org/wiki/Maghemite
168159a3.png
f9bbbf72.png

Overview
Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxides. It has the same spinel ferrite structure as magnetite and is also ferrimagnetic.
Maghemite can be considered as an Fe(II)-deficient magnetite with formula where represents a vacancy, A indicates tetrahedral and B octahedral positioning.
I don't think so, I think it unlikely that you would see streaks of what looks like quartz through it as in the OP's sampleD
 

Attachments

  • 168159a3.png
    168159a3.png
    146 bytes · Views: 550
  • f9bbbf72.png
    f9bbbf72.png
    158 bytes · Views: 560
  • Like
Likes C Mac
  • #9
Thank you for the feedback and great leads. (Yes, I had to google maghemite as well.) In addition, it really looks like gneiss (pictured above) with quartz banding. Of course, it also looks similar to the photo of magnetite, minus the crystals. Thanks for narrowing it down.

Hope the forum doesn't mind if I post a few more rocks that I've come across.
 
  • Like
Likes davenn
  • #10
C Mac said:
Hope the forum doesn't mind if I post a few more rocks that I've come across.
All good :smile: use a different thread for each sample just to keep comments/replies together for a particular sample
 
  • Like
Likes C Mac

1. Where can I find resources for identifying rocks in the Southwestern US?

There are several resources available for identifying rocks in the Southwestern US. One option is to consult a local geology guidebook or field guide specific to the region. You can also visit a local rock and mineral club or museum for assistance. Online resources such as geology websites or forums can also be helpful.

2. What characteristics should I look for when trying to identify a rock?

When identifying a rock, it is important to look at its color, texture, hardness, and any visible minerals or crystals. You can also try to determine the rock's composition and whether it is igneous, sedimentary, or metamorphic in origin.

3. How can I tell the difference between a rock and a mineral?

Rocks are made up of one or more minerals, so they can be distinguished by their composition. Minerals are naturally occurring substances with a specific chemical composition and crystal structure, while rocks are made up of a combination of minerals and other materials.

4. Are there any common rocks found in the Southwestern US that are easy to identify?

Yes, there are several common rocks found in the Southwestern US that are relatively easy to identify. These include sandstone, limestone, shale, and basalt. However, it is important to note that there can be variations in these rocks depending on the specific location.

5. Can I use a phone app to identify rocks?

Yes, there are several phone apps available that can assist with rock identification. These apps use photos and descriptions to help identify rocks and minerals. However, it is always best to consult with a trained geologist or use multiple resources for a more accurate identification.

Similar threads

Replies
6
Views
3K
  • Sci-Fi Writing and World Building
Replies
21
Views
1K
  • STEM Academic Advising
2
Replies
54
Views
4K
Replies
10
Views
2K
  • STEM Academic Advising
Replies
9
Views
9K
Replies
4
Views
9K
  • STEM Academic Advising
Replies
1
Views
1K
  • General Discussion
Replies
26
Views
9K
Replies
5
Views
2K
Back
Top