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Permeable soil
Permeable soil
A soil that lets water pass through it easily. It is the equivalent to well- drained soil. Most soils that contain sand and are rich in humus and calcium are well drained.
Petroleum
The carbon rich, and mostly liquid, mixture produced by animal and plant remains that have been buried and transformed by heat and pressure over long periods of time.
Petroleum is found in many sedimentary rocks. The liquid part of petroleum is called oil; the gaseous part is known as natural gas. Petroleum is an important fossil fuel. (See also: Impermeable; Petroleum field; Reservoir rock.)
Petroleum field
A region from which petroleum can be recovered.
 Petroleum – Petroleum occurs naturally in a number of rock structures where it becomes trapped. These are shown on this diagram.
pH
A measurement of acidity. On
the pH scale, each number lower down indicates a tenfold increase in acidity. Neutral on the scale
is 7. Numbers larger than 7 are alkaline, and values less than 7 are acid. Normal soils range from pH 4 to pH 8.
Phenocryst
An especially large crystal embedded in smaller mineral grains.
Placer deposit
A sediment containing heavy metal grains (for example, gold) that have weathered out of nearby rocks and are concentrated in
a stream bed or along a coast. Gold and tin are two elements commonly recovered from
placer deposits. Most historic
gold rushes were based on
placer deposits rather than on lodes. (See also: Diamond.)
A cap rock is impermeable to oil or natural gas.
Acid
Alkaline
 pH – Soils are measured by their acidity or pH. Each
pH level produces a characteristic colour
when special indicator chemicals are added. The
redder the colour, the more acid and the greener
the colour, the more alkaline a soil is.
Petroleum wells are drilled down to the traps.
Petroleum can be trapped in rocks pushed up by a salt dome.
Petroleum can be trapped in the top of an anticline or dome.
Petroleum can be trapped in a permeable rock against a fault.
Petroleum can be trapped in a permeable rock against an unconformity.
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