You are here:

Geology/rock problem

Advertisement


Question
puzzling rock
puzzling rock  
I have a black-and-white striped rock with gold and silver sparkles on it, and I wish to know what it is it is bothering me very much and I need to use it for fair on my rocks and minerals project. If you want me to I could probably send a picture and if I can figure it out. I don't have much time left.

Answer
Timmy:

The rock looks like and sounds like a mica gneiss.

The sparkles are mica either biotite or muscovite.  They are the same flat mineral that sticks to your skin at the beach.

The banding is usually caused by alignment of quartz and other minerals in foliation bands.

It is a metamorphic rock and is formed by compressive stresses on another pre-existing rock causing the original minerals to recrystallize and align perpendicular to the applied stress.  So the bands run at right angles to the direction the stress waa applied.

So in a plate tectonic sense the rock was squeezed by mountain building forces or plate forces causing the bands to form.  The bands and foliation or alignment of the minerals was in response to the squishing forces placed upon it.

The lighter bands are probably quartz and the darker bands are mafic containing more iron or magnesium.  
such as pyroxene, amphibole, or biotite.  In your case it sounds like it it rich in biotite, the sparkly stuff.

Geology

All Answers


Answers by Expert:


Ask Experts

Volunteer


Keith Patton

Expertise

I can answer questions concerning physical and historical geology, environmental geology/hydrology, environmental consulting, remote sensing/aerial photo interpretation, G&G computer applications, petroleum exploration, drilling, geochemistry, geochemical and microbiological prospecting, 3D reservoir modeling, computer mapping and drilling.I am not a geophysicist.

Experience

I have 24 years experience split between the petroleum and environmental industries. I have served as an expert witness in remote sensing, developmental geologist, exploration geologist, enviromental project manager, and subject matter expert in geology and geophysical software development.

Organizations
American Association of Petroleum Geologists
American Association of Photogrammetrists and Remote Sensing

Education/Credentials
Bachelor and Master of Science
Registered Geologist in State of Texas

©2016 About.com. All rights reserved.