Rocks, Minerals, and Fossils

Goal

This is not only designed for all of the awesome rocks, minerals, and fossils that catch your eye while you are hiking or climbing in the mountains, but also to try and spread some educational geology, mineralogy, and paleontology about what is in the pictures.

It is always good to know the history of the area and rocks, much like it is important to know the history of a particular climb. This is on a smaller scale than larger features you see in the rocks,(such as faults, monoclines, etc.) these can be posted on the Geologic Structures Album .

Any information on how the item formed, what formation it is part of, or how old it is would be greatly appreciated. It would be great to include a scale in the picture or caption if possible. Enjoy!

Definitions

Rocks:

A rock is an aggregate of one or more minerals. (A rock may also include organic remains and mineraloids.) Some rocks are predominantly composed of just one mineral. For example, limestone is a sedimentary rock composed almost entirely of the mineral calcite. Other rocks contain many minerals, and the specific minerals in a rock can vary widely.

Some minerals, like quartz, mica or feldspar are common, while others have been found in only one or two locations worldwide. The vast majority of the rocks of the Earth's crust consist of quartz, feldspar, mica, chlorite, kaolin, calcite, epidote, olivine, augite, hornblende, magnetite, hematite, limonite and a few other minerals.[4] Over half of the mineral species known are so rare that they have only been found in a handful of samples, and many are known from only one or two small grains.

Minerals:

A mineral is a naturally-occurring, homogeneous substance with a defined chemical composition and structure. Traditional definitions excluded organically derived material.

Chemical composition may vary between 'end members' of a mineral system. End members are essentially the same mineral with a different percentage of a cation combination. For example the plagioclase feldspars comprise a series from sodium-rich albite (NaAlSi3O8) to calcium-rich anorthite (CaAl2Si2O8) with four recognized intermediate compositions between.


A crystal structure is the orderly geometric spatial arrangement of atoms in the internal structure of a mineral. There are 14 basic crystal lattice arrangements of atoms in three dimensions, and these are referred to as the 14 "Bravais lattices". Each of these lattices can be classified into one of the six crystal systems, and all crystal structures currently recognized fit in one Bravais lattice and one crystal system. This crystal structure is based on regular internal atomic or ionic arrangement that is often expressed in the geometric form that the crystal takes. Even when the mineral grains are too small to see or are irregularly shaped, the underlying crystal structure is always periodic, and can be determined by X-ray diffraction.

Chemistry and crystal structure together define a mineral. Two or more minerals may have the same chemical composition, but differ in crystal structure (these are known as polymorphs). For example, pyrite and marcasite are both iron sulfide, but their arrangement of atoms differs. Similarly, some minerals have different chemical compositions, but the same crystal structure: for example, halite (made from sodium and chlorine), galena (made from lead and sulfur) and periclase (made from magnesium and oxygen) all share the same cubic crystal structure.

Crystal structure greatly influences a mineral's physical properties. For example, though diamond and graphite have the same composition (both are pure carbon), graphite is very soft, while diamond is the hardest of all known minerals. This happens because the carbon atoms in graphite are arranged into sheets which can slide easily past each other, while the carbon atoms in diamond form a strong, interlocking three-dimensional network.

There are currently just over 4,000 known minerals, according to the International Mineralogical Association, which is responsible for the approval of and naming of new mineral species found in nature. Of these, perhaps 150 can be called "common," 50 are "occasional," and the rest are "rare" to "extremely rare."

Fossils:

The word fossil come from the Latin fossus, literally "having been dug up". They are the mineralized or otherwise preserved remains or traces (such as footprints) of animals, plants, and other organisms. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous rock formations and sedimentary layers (strata) is known as the fossil record.

The study of fossils across geological time, how they were formed, and the evolutionary relationships between taxa (phylogeny) are some of the most important functions of the science of paleontology.

Using radiometric dating techniques,(such as K-Ar and Pb-U) geologists have determined most fossils to be several thousands to several billions of years old. Fossils vary in size from microscopic, such as single cells, to gigantic, such as dinosaurs.
[img:277522:aligncenter:small:A paleocene (Torrejonian in age) leaf found in the San Juan Basin, NM.]

A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous exoskeletons of invertebrates. Preservation of soft tissues is exquisitely rare in the fossil record, although there are many fine examples today.

Fossils may also consist of the marks left behind by the organism while it was alive, such as the footprint or feces of a reptile. These types of fossil are called trace fossils (or ichnofossils) as opposed to body fossils.

Finally, past life leaves some markers that cannot be seen but can be detected in the form of biochemical signals; these are known as chemical fossils or biomarkers.


Sources:

Introduction to Mineralogy, William D. Nesse

The Present in the Key to the Past, Hugh Rance

Wikipedia

Links

A good site for Historical Geology .

A good site for Mineralogy.

Images

View Rocks, Minerals, and Fossils Image Gallery - 235 Images