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Geology/magnetic field


I have an area that has a stong underground magnetic field, it is located in a very rural area with no underground piprs or lines.  The soil is black clay, when I dug down in the soil it has something in it that looks like small gray flakes.  The property is in central Texas. Is there a home test I can use to determine if the gray is metalic?

There is a very simple test for many metallic minerals; it requires a magnet.  Many metallic minerals are also attracted by magnetic fields.  

If the soil is black then there is most probably a high carbon content.  If there is a significant carbon content the gray flakes are probably not magnetic but are Muscovite.  Muscovite (also known as mica, isinglass, or potash mica) is a phyllosilicate mineral of aluminium and potassium with formula KAl2(AlSi3O10)(F,OH)2, or (KF)2(Al2O3)3(SiO2)6(H2O). It is the most common of all micas and is common in most sedimentary rocks; having been generally eroded from igneous or metamorphic rocks.

Muscovite has a highly-perfect basal cleavage yielding remarkably-thin laminæ (sheets) which are often highly elastic. Sheets of muscovite 5×3 m have been found in Nellore, India.
Muscovite has a Mohs hardness of 2–2.25 parallel to the [001] face, 4 perpendicular to the [001] and a specific gravity of 2.76–3. It can be colorless or tinted through grays, browns, greens, yellows, or (rarely) violet or red, and can be transparent or translucent. It is anisotropic and has high birefringence. Its crystal system is monoclinic. The green, chromium-rich variety is called fuchsite; mariposite is also a chromium-rich type of muscovite.

Muscovite is the most common mica, found in granites, pegmatites, gneisses, and schists, and as a contact metamorphic rock or as a secondary mineral resulting from the alteration of topaz, feldspar, kyanite, etc. In pegmatites, it is often found in immense sheets that are commercially valuable. Muscovite is in demand for the manufacture of fireproofing and insulating materials and to some extent as a lubricant.  The name of muscovite comes from Muscovy-glass, a name formerly used for the mineral because of its use in Russia for windows.

If you can find a microscope, get the largest piece that you can find and try to scratch it while looking at it under the microscope.  It should scratch easily, if it is muscovite, in fact it may be scratched with your fingernail since your fingernail has a hardness of 2.5 and muscovite's hardness is between 2 and 2.5.


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Joe Norris


I am an economic geologist. An economic geologist does mineral evaluations and appraisals of mineral or mining properties. I can tell you if your deposit has value - remember that a mineral deposit, no matter how good, only has value when mined. Any value assigned to a mineral deposit, in the ground, is only the speculative value that deposit.


I have been a economic geologist for most of my 35 year career. Although I have done work in perhaps 45 states and numerious countries much of my work has been in Appalachian coal, intermountain west gold and silver, and Arizona uranium.

Past President of the Virginia Section of the American Institute of Professional Geologists and a certified geologist in twelve states.

BS Degree from Eastern Kentucky University. Work on MS Degree @ Eastern Kentucky University, Colorad School of Mines & Marshall University Numerious short courses on the value of mineral deposits and how to value same. Also several short courses dealing with the different types of geologic processes; sedimentary, igneous, metamorphic along with the mineral associated with each.

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