You are here:

Geology/can you help me identify this rock


concave side up
concave side up  

concave side down
concave side down  
Thanks for helping me/ This rock from north Cascades Mtn range Wa State [western] I found at bottom area of gradient as alluvial deposit [or start of alluvial fan] from mountain creek/ This rock looks "molten" and unlike most other rocks that are rounded as old river deposits/ It weighs 12lbs/ has no cleavage [ie shist/gneiss] but resembles "large, greenish oyster shell in contour/shape"the underside has goldish/iron/rusty-like specs [which is concave underside: From mainly Mesozoic/Crystalline/metamorphic period [CASCADE MTNS]/ The closest active volcano is Glacier Peak to south and Mt Baker to north/ Thank you for helping me!

Hi Brad,
Interesting looking rock, and you've given much information, but the image is very blurry so I can't tell much from it.  However, I get the feel, from what I can make out, that it's probably a glauconite rich mica schist.  The rusty looking specs (biotite/muscovite# and greenish color #glauconite# allow me to lean toward that ID.  Also, as you mention, the Cascade Range is rich in metamorphic rocks.  It's not volcanic.  The "molten" appearance is due to a characteristic of most schists#  What happens is, the temp and pressures force the minerals in the rock into "layers" #well, not really "layers" we call them foliations, but "layers" make a better description) and orient them so they seem to flow#  The rock can look very much like it was molten#

Here's some examples of mica schists#  They aren't as good as I'd like, but I think they will show what I mean:


Hope this helps.


All Answers

Answers by Expert:

Ask Experts


C. Robert Reszka, Jr.


I can answer any general geology question (rocks, minerals, stratigraphy, geomorphology etc.). My expertise is in the geology of the Michigan Basin, PreCambrian, Paleozoic and Recent. I can answer questions concerning mining and petroleum exploration and production and the laws concerning those activities. I can also answer questions concerning stratigraphy of the Michigan Basin. I will also answer questions about mineral and rock collecting in the Basin. I won`t be able to answer many specific questions on hydrology, geophysics or geochemistry. I may be able to answer very general questions in those venues.


I have been working for the State of Michigan for 36 years as a Geologist and a Resource Analyst. I have experience with Subsurface Geology and Petroleum Geology, mining in Michigan, and Sand Dune Mining and Protection issues.

Michigan Basin Geological Society

Decade of North American Geology.
Bedrock Geology of Michigan

BS Wayne State University

©2017 All rights reserved.