how to figure out what rock you have

Stone Identiification Nuts

Rock Identiification Basics

Rock Origin
Stone Limerick
Rock Texture
Geological Principals
Geological Time
Common Exploration Terms
run across slso Igneous rocks...
see too Sedimentary rocks...
see also Metamorphic rocks...
see likewise Geological fourth dimension...
meet as well Absolute time...

To identify
a stone, iii things must be considered:

1. origin,
2. composition,  and
3. texture.

Rock Origin

The showtime pace to identify a rock is to try to categorize the rock into ane of the three main types or groups of rocks.
These include igneous, sedimentary or metamorphic types.
The simply rocks which do not fall into one of these categories are meteorites.
Igneous, sedimentary and metamorphic stone types are distinguished by the processes which form them.

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Igneous rocks:
form past crystallization of a melt (molten rock fabric).
Subcategories:

Plutonic:
formed at significant depth beneath the surface.

Volcanic:

formed at or about the surface.

Sedimentary rocks:

grade by the compaction small or large grains or fragments of pre-existing rocks, or past the atmospheric precipitation of mineral matter from a body of h2o, such equally an bounding main, lake or stream.

Metamorphic rocks:
formed from pre-existing igneous, sedimentary or metamorphic rocks by subjecting them to heat and/or pressure and/or migrating fluids, causing the original mineral assemblage of the stone to modify to a new assemblage of minerals. The origin is not e'er obvious, but sufficient training will enable recognition of certain features which point to the nigh probable origin. Examples include the common presence of bedding or layering in sedimentary rocks, and the presence of mineral foliations or lineations in metamorphic rocks. One must also consider the geologic surroundings where the rock is found.

For example, in a young volcanic terrane one is less likely to find sedimentary or metamorphic rocks.
When the origin is completely unobvious, the composition and texture must be relied upon to brand the all-time guess.

Download Identification of Common Rocks .pdf  from this site...

Rock Composition

The rock limerick is found past determining which minerals brand upwardly the rock.
Past definition, a rock is a solid mass or compound consisting of at to the lowest degree ii minerals (although in that location are some exceptions when a rock may consist entirely of one mineral). The minerals comprising the rock can be identified using common field testing methods for individual minerals, particularly where the texture is sufficiently fibroid-grained enough to distinguish the private minerals with the naked centre or a hand lens.

Where the grain size of the minerals comprising the stone are too fine-grained to recognize detached minerals, "petrographic" methods (those using a microscope) can be used for reliable identification in many cases.
Petrographic methods involve the utilize of a microscope to examine the optical properties of discrete minerals magnified through the microscope lens.
Properties include the behavior of refracted, reflected and transmitted light either through a thin wafer piece of the rock (called a thin department), or of a sample plug (for reflected light).
The light source is adjusted to provide light which polarized in one or two directions.

Unlike minerals have characteristic optical properties, which can be used with tables of optical mineral properties to identify the mineral.
Other instruments which can be used to make mineral identification include the electron microscope.
These methods are reliable but expensive, and require somewhat tedious sample training.
The image is obtained past exposing the sample to electron battery and imaging the results.

X-Ray Diffraction Techniques
Another method to place small mineral grains is using X-ray powder diffraction.
A modest amount of cloth is ground into a powder and bombarded with 10-rays.
The results are recorded on a moving picture strip in a camera, or in the form of graph.
The reflections of the 10-rays are measured to determine the 'd-spacings' of the unknown mineral.
Each mineral has a unique set of peaks corresponding to d-spacings, which are related to the crystal structure.
In X-ray spectrometry, another method to place minerals, the X-rays cause the emission of photons from the surface of the mineral.
The sample is prepared by obtaining a very high polish on its surface.
The photons emitted from the surface atoms accept characteristic energies for specific elements.
By measuring the energy levels of the photons, the mineral composition can be identified.

Rock Texture

The texture of a rock is defined past observing two criteria:1) grain sizes,ii) grain shapes.

Grain Size:
the boilerplate size of the mineral grains.
The size scale used for sedimentary, igneous and metamorphic rocks are unlike

Grain Shape:
the general shape of the mineral grains (crystal faces evident, or crystals are rounded).
Examples of the size classifications for each of the iii major rock types include:

FINE-GRAINED

> > > > > > > > > > > > > > > >

Fibroid-GRAINED
Sedimentary

: Shale Siltstone Sandstone Wacke Conglomerate

Metamorphic

: Slate Phyllite Schist Gneiss

Igneous

: Rhyolite Granite

Stone Type	Very Fine Grained	Fine Grained	Medium Grained	Coarse Grained	Very Fibroid Grained
Clastic Sedimentary	.06 - .125 mm	.125 - .25 mm	.25 - .5 mm	.5 ­ i mm	i ­ 2 mm
Metamorphic		< .25 mm	.25 ­ 1 mm	i ­ two mm	> two mm
Igneous		< i mm	1 ­ 5 mm	5 ­ 20 mm	> 20 mm

Sizes are median diameter of grains in millimeters.

Geologic Principles

One of the main goals of mineral exploration is to predict the geometry and relationships of different rock types nether the surface where they can't exist seen either below the surface or beyond the immediate exposures.
This is essential to know in society to plan a mine.
Much try and a diversity of techniques are used to analyze the timing or "geologic history" of the area

In that location are iii primary principles, or "laws", which are used in field geological studies to guide in determining the relative timing of events. Law of Cross-cut Relationship

The "Police of Cross-cutting Relations" is a principle which is useful to use in igneous provinces.
It states that invading rocks are younger than those invaded.
For instance,
an igneous dike invading a sedimentary or metamorphic rock.
Some other case is a state of affairs where in that location are multiple intrusions are establish; the sequence of igneous events can be sorted out by observing which intrusions cut which other intrusions.
The sequence might give an indication of a particular differentiation pattern of the magma.
The same law applies to veining relationships:younger veins cut across older vein sets
Often times where there are gold-bearing quartz veins at that place are likewise other veins which are barren, and may take a different orientation due to unlike structural conditions during formation.

Vein crosscutting relations.
Vein A is cutting by Vein B.
Vein C cuts both A and B, so it is youngest. Law of Superposition
The "Law of Superposition" is a law which applies to sedimentary rocks.
It states that where undisturbed, layered, sedimentary rocks occur, younger rocks volition be situated on meridian (above) older rocks.
The same law tin apply to layered volcanic flows, where the ages of the succeeding layers going up section volition exist relatively younger than the lower function of the section.
This law is too 1 which is employed to determine age relationships of different stone units.
In mineral exploration, a situation where this principle could be employed would exist to project the underground geometry of a mineralized or petroleum enriched formation.

Principle of Uniformitarianism
The "Principle of Uniformitarianism" states that the earth is a result of natural forces which are presently active and have persisted over the course of geologic time.
Rocks course nearly ofttimes every bit a consequence of slow, gradual developments resulting from various geologic processes.
Catastrophic events do occur and contribute to the overall development and history of rocks, but these events are less frequent and contribute to only a small percentage of the cyberspace upshot of natural forces in general.
This principle has been used to written report the history of ancient volcanic rocks past observing present day volcanic action.
For example, a sure type of massive sulfide eolith has been documented forth an active body of water flooring rift.
This cognition tin can be used to better understand a certain type of Copper-Lead-Zinc ore deposits, called "volcanogenic massive sulfide depsits", or "VMS".

Geologic Time

see also Some rocks exposed at the surface are very young, but well-nigh are very old, in fact are much older than the historical records of humanity.
These "former" rocks are generally many millions of years in age.
The vastness of the concept of 'millions" of years tin be difficult to encompass since human being life times are so much shorter (generally less than 100 years).
Units of geologic time which take established include the "era" (longest), "menstruation", and "epoch" (shortest).
All of geologic fourth dimension has been divided into 4 main eras, chosen (from oldest to youngest) the Precambrian, the Paleozoic, the Mesozoic and the Cenezoic.
Sites 1 ­ half dozen provide illustrations and summaries of the geologic time scale. The globe has slowly changed throughout its history, and continues to exercise so as a result of a very ho-hum cooling and differentiation process.
As a result, certain time periods during the earth's history had weather condition more conducive to formation of specific types of mineral deposits (Site 7).
For this reason, knowing the guess age of rocks can be a crude guide to the types of mineral deposits most likely to be plant. When evaluating the ages of rocks nosotros speak of two types of terms of ages chosen "accented age" and "relative age".
"Absolute historic period" is measured in years, and depends on having some type of fourth dimension scale to mensurate confronting, typically by using a highly technical chemical dating method.
"Relative age" simply ways placing i geologic result or feature in context with another in a timing sequence.
Accented Age:
During the early on 1900's, shortly after the discovery of radioactivity, it was discovered that radioactivity involves the transformation of radioactive atoms into completely different elements.
Each radioactive substance disintegrates at its ain rate and forms a unique prepare of girl products (elements).
The charge per unit of decay is generally very slow.
For case, uranium changes into lead at a charge per unit such that half of the original amount will be converted to lead after a period of 4,500 meg years.
Half of the remaining uranium volition convert to lead in some other 4,500 million years, and then on.
Therefore the "half life" of uranium is 4,500 meg years.
By measuring the ratio of unchanged uranium to lead in a sample, and knowing the rate of decay, we can calculate the length of time the sample has been disintegrating, or in other words, the age of the rock.
Besides the Uranium-Lead method, several other radiometric techniques are bachelor, including Carbon 14 and Rubidium-Strontium.
Relative Age Where different rocks are in concrete contact and observable, the relative ages of the rocks can oftentimes exist determined evaluating superposition and cross-cut relationships.
Rocks comprising the upper strata are younger than rocks comprising the lower strata.
Rocks formed from an intruding magma are younger than the rocks they intrude.
Inclusions within an igneous rock are older than the magma which formed the matrix. When dissimilar rocks are in close proximity but their actual contacts are non visible, a geologic map and cross-section can be made which illustrate the geometric relationships of the rocks, and allows the conclusion of relative historic period. Difficulty is encountered when attempting to correlate rocks which are not in direct contact or fifty-fifty close proximity.
Fortunately geologists have worked out the evolutionary succession of fossil forms.
It was establish that sedimentary rocks containing fossils could easily be placed in a successive sequence with respect to time by identifying the fossil assemblages present.
The natural outgrowth of this effort was to begin comparing rocks from all parts of the globe.
Fossils could now be used to attach relative ages to a wide variety of different sedimentary rock types.
They have been used to construct what is referred to equally the "Geologic Time Scale", which is a chronology of the earth's history largely based on the fossil tape. Since the oldest rocks and the oldest fossils are the ones about likely to become obliterated due to age, nosotros have much more fossil information available for younger rocks, and hence these contain the smallest subdivisions of time.
The Paleozoic Era was when invertebrates and simple vertebrates (fish, amphibians and primitive reptiles) were the ascendant life forms.
The Mesozoic Era was when reptiles, including the dinosaurs, ruled.
The Cenezoic Era is best characterized as the time when mammals became ascendant.

Exploration Geology Terms

The following terms are useful to know:
Ore:
the rock material or minerals which are mined for a profit.
Ore Minerals:
the specific minerals inside the ore which contain the metals to exist recovered.
Gangue Minerals:
the minerals having no commercial value, they just happen to be mixed upwardly with the ore minerals.
Prospect:
potential ore eolith, based on preliminary exploration.
Mine:
Earthworks for the extraction of mineral deposits, either at the surface (open pit mine) or below (underground mine).
Orebody or Ore Deposit:
naturally occurring materials from which a mineral or minerals of economical value tin can be recovered at a reasonable turn a profit.
Mineral Deposit:
similar to an ore eolith, simply is implied to be subeconomic or incompletely evaluated at present.
Mineral Occurrence:
anomalous concentration of minerals, but is uneconomic at present.
Class:
this ways the concentration of the substance of involvement, usually stated in terms of weight per unit of measurement book.
Cut-off Grade:
the lower limit of concentration adequate for making a turn a profit when mining.
Host Rock:
the rock lithology (blazon) which contains the ore.
May or may non contain ore.
State Rocks:
the rocks of no commercial value surrounding the host rocks and/or the ore.
Anomalous:
above or beneath the range of values considered to exist normal.

source Delta Mine Training Centre
http://geologycafe.com/gems/chapter3.html

garnerpomed1946.blogspot.com

Source: http://earthsci.org/mineral/rockmin/identification/identification.html