ROCKS
THE BUILDING BLOCKS OF THE EARTH
Mining and Exploration
Geology Handbook
Rocks – the building blocks of everything
Geology is the science that deals with the physical history and dynamics of the earth and the rocks it is composed of. Rocks are important – everything we have is derived from mining or grown (in soil which is mostly broken down rocks).
To define what a rock is, we need to look at what makes up a rock.
Elements, as in the periodic table of, are the simplest substances made up of molecules. They cannot be broken down or easily converted into another element. Elements come from stars, all elements heavier than iron (Fe), come from supernovae. Everything is made of elements, We are made from stardust.
When elements combine to form more complex crystalline materials using natural processes, you get minerals. Minerals can be simply an element (gold – Au), or complex (Feldspar – CaAl2Si2O8).
Minerals are defined if and only if they are naturally occurring, crystalline in nature, have a defined chemical structure.
Rocks are combinations of one or more minerals and may contain other compounds with a complicated chemical structure.
mINERALS
The basic building blocks of rocks everywhere. The minerals in each rock tell the story of the history of that rock and the envireonment in which it formed.
IGNEOUS
Rocks formed from the full melting and mixing deep in the earth. They form crystalline structures of various sizes as the molten material (lava/magma) cool. The longer it takes to cool, the larger the crystals. Mafic rocks make for great source rocks for valuable mineral deposits.
SEDIMENTARY
As rocks buried in the earth become exposed at the surface, wind, water, ice, chemical and all sorts of reactions try to break down and reduce that rock to the smallest bits possible. These bits form sediments (sand, silt, clay) and eventually will accumulate somewhere (rivers, oceans, etc) where they will over time solidify into a new rock
METAMORPHIC
These rocks are what happen when you take any rock and expose it to increased temperature (proximity to molten rock), pressure (burying) or combination of the two. The increased pressure, temperature as well as the environment and chemical makeup will cause the old rock to change into a new rock. Some minerals will change, new elements/minerals are introduced martial melting takes place. The rock is chemically and physically changed from its source rock.
Identify and Classify
Basic rock identification and classification.
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BASIC ROCK CLASSIFICATIONS
Of primary importance to the mining world are the two main types of igneous rocks.
Mafic: The dark, heavier rocks. What makes them heavier? Heavier minerals, heavier minerals tend to be the ones most sought after for mining (metals). These rocks form the oceanic crust. with the lighter Felsic continental crust “floating” on top. Mafic rocks are the source of most valuable mineral deposits.
Felsic: Literally lighter rocks, high in silica, form continental crust. Granite is a perfect example.
Of additional importance to the mining world are the three main types of sedimentary rocks.
Chemical: Formed from evaporation of standing water (ex. Salt, Gypsum)
Organic: Organic matter or debris (ex. Chalk, Limestone)
Clastic: Everyday broken down chunks of rock washing down rivers. (ex. Sandstone, Siltstone)