Rocks, Fossils, and Minerals for Sale
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If you're hunting for Rocks, Minerals, and Fossils, you've hit the Mother Lode!  At Mother Lode Rock Shop, you get to pick.  Choose the exact specimens you want from our wide-ranging collection of Rocks, Minerals, and Fossils.

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Geology 101

Minerals     Rocks and the Rock Cycle Plate Tectonics
Geologic Time Scale Fossils and How They Form  Fossil Stratigraphic Ranges

Minerals are the building blocks of rocks.  A mineral is a naturally occuring solid compound usually composed of two or more chemical elements.  A few minerals, such as copper, gold, silver, and sulfur, occur as single "native" elements. Minerals are defined both by their chemical formula and by their internal crystal structure.  For example, iron sulfide has the formula FeS2, where F is iron and S is sulfur.  Iron sulfide, like many other minerals, can crystallize in different ways.  When it crystallizes in a cubic system, it forms the mineral pyrite.  When it crystallizes in an orthorhombic system, it forms the mineral marcasite.

    Learn more about mineral crystal systems.

    Watch this 10-minute video to learn more about minerals:

The Mohs Hardness Scale is a qualitative scale used to rank the hardness of a mineral by comparing its scratch resistance to other minerals.  It was developed in 1812 by the German geologist Friedrich Mohs.
Hardness Mineral Notes
1 Talc Very easily scratched by a fingernail
2 Gypsum Can be scratched by a fingernail
3 Calcite Just scratched with a copper coin
4 Fluorite Very easily scratched with a knife
5 Apatite Scratched with a knife with difficulty
6 Orthoclase Cannot be scratched with a knife but scratches glass with difficulty
7 Quartz Scratches glass easily
8 Topaz Scratches glass very easily
9 Corundum Cuts glass
10 Diamond Cuts glass

Rocks and the Rock Cycle

A rock is a naturally occurring aggregate of one or more minerals.  Rocks are classified into 3 basic categories: igneous, sedimentary, and metamorphic.
  • Igneous rocks form from molten rock (lava or magma).  Examples include granite and basalt.
  • Sedimentary rocks form by the deposition of organic or inorganic material, either from sediments formed by the weathering and erosion of other rocks, or by chemical precipitation from a solution.  Deposits are laid down by water, wind, or ice, usually in layers or strata.  Examples include sandstone and limestone.
  • Metamorphic rocks form when the composition, texture, or structure of existing rock is changed by extreme temperature, extreme pressure, or both.  Examples include slate and marble.
   Learn more about the three different rock types

The process by which rocks are formed, eroded, and reconstituted into new rocks is called The Rock Cycle.

Rock Cycle
Image courtesy of U.S. Geological Survey


Plate Tectonics

The rigid outer shell of the Earth, called the lithosphere, is broken into giant slabs of rock called tectonic plates.  The plates move gradually over time, driven by convection currents inside the Earth's mantle.

The U.S. Geological Survey's online presentation, This Dynamic Earth: The Story of Plate Tectonics, provides an excellent overview.

This Dynamic Earth
Image courtesy of U.S. Geological Survey

Geologic Time Scale

The Earth's history is divided into time intervals called Eons, Eras, and Periods.  The boundaries between each interval reflect important events, such as global extinctions of plant and animal species, or the first appearance of certain species on the fossil record.

Geologic Time Scale
Image courtesy of U.S. Geological Survey

Here's a printable Geologic Time Scale.


What Is a Fossil and How Do Fossils Form?

The following web sites have excellent explanations:

The Virtual Fossil Museum

American Geosciences Institute


Stratigraphic Ranges of Major Species in the Fossil Record

Fossil Succession Chart
Image courtesy of U.S. Geological Survey

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Mother Lode Rock Shop
PO Box 1812
Nevada City, CA 95959