• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Classifying Igneous Rocks

Extracts from this document...


CLASSIFYING IGNEOUS ROCKS An igneous rock is a rock formed by the cooling and crystallization of magma intrusively in the crust or extrusively on the surface. The location and speed of cooling and the type of magma determine which igneous rock is formed. Igneous rocks can be classified according to their colour, texture and density, the minerals present, and the chemical composition of the rock. COLOUR Colour is useful as a diagnostic tool for course-grained igneous rocks but not fine grained. The colour index of a rock indicates the amount of dark ferromagnesian minerals that are present. These include olivine, pyroxene and biotite mica. They are rich in iron and magnesium and usually associated with constructive plate margins. ...read more.


* Fine-grained igneous rocks have grain sizes of less than 0.25mm. (the crystals are not distinguishable with the naked eye and a hand lens is needed for identification). These cool quickly on the surface (extrusive) and are known as volcanic rocks. They commonly form in lava flows. An example of a fine grained igneous rock is basalt * Medium grained rocks have a grain size of 0.25-2mm. (The crystals can be seen with the naked eye but a hand lens is needed for identification). They commonly form in dykes and sills. These rocks are known as hypabyssal. Eg. Dolerite * Course grained igneous rocks have a grain size greater than 2mm. ...read more.


* Flow-banded: These rocks show a rough banding of lava constituents. The bands are highly contorted and continuous for several cms. Flow-banded rocks are commonly associated with viscous lavas. * Amygdaloidal: when vesicles in the rock have been filled in by later generations of crystals. MINERAL COMPOSITION The main minerals in igneous rocks are: Olivene, pyroxene, amphibole, biotite and muscovite micas, quartz, plagioclase and orthoclase feldspars. Which minerals are present in a particular rock depend on temperature, viscosity and plate tectonic context. Recurring mineral groupings are called mineral associations. Studying these enables us to predict which minerals may occur together in a rock and which are mutually exclusive. The main minerals present in an igneous rock are known as the essential minerals of that rock. These have a common temperature crystallisation range and so are commonly found together. Minerals present in small amounts are called accessory minerals. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Rocks & Weathering section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Rocks & Weathering essays

  1. Sedimentary Rocks

    It the substances is limestone, carbon dioxide should be given off. When hydrochloric acid is added to limestone, it the solution should fizz giving off a colourless gas that turns limewater milky, which is carbon dioxide CO2. Calcium carbonate + Hydrochloric acid = Calcium chloride + water + carbon dioxide

  2. Determining the paleoenviroment and tectonic history of a small area (Cocklawburn Beach)

    by differing sea levels at the time of deposition, for example, if the cyclotherms that is composed of bed 1-5 is examined, then the pattern is: 1: Limestone - Deep Sea where dead creatures decomposed to form limestone layers 2-3: Silt - Shallowing seas mean layers are formed by fine

  1. 'I think that sedimentary stones will be more affected by weathering than igneous stones.' ...

    or merely weaken it so that it is more prone to other kinds of weathering. - There is also another kind of biotic weathering from the lichen that stick to the gravestones, because they secrete an acid onto the stone in order to extract its minerals and this weakens the stone.

  2. Construct two Graphic Log Sections, one on the eastern exposure (ST 3375 6645) and ...

    14 Limestone, mud, soft sandstone. Red and soft and very fine grained. Laminations, chert nodules/bands. Faulting and asymmetrical ripple marks. Faulting, the surface has moved. Asymmetrical ripple marks could have been formed by a meandering river or delta. Unidirectional current movement over sediment causing sediments to build up into ridges which tend to have one long shallow slope and one short steep downstream slope.

  1. Maggies Rock.

    The watchful eye of a huge crescent shaped bright yellow moon was overlooking this most wondrous setting. Mum and I soon settled into country living, like ducks to water mum said. Everyday before and after school I would help mum in the teashop, observing the villagers and their quaint ways, they had not accepted us yet.

  2. Classification of Igneous rocks.

    * Batholiths * Limited nuclei-, which grow to bigger crystals- ionic diffusion. * Example- Granite Medium= * 1-5mm- crystals are visible with the naked eye, but you may need a hand lense to identify them. * Medium rate of cooling.

  1. James Hutton (1727-1797), the eminent 18th century gentleman farmer and founder of modern geoscience, ...

    igneous rocks form at sea floor spreading ridges. Fluid intrusion of these rocks, both during and after formation, results in some low grade metamorphism. As the rocks cool, and more magma is introduced from below, the plate is forced away from the spreading ridge, and acquires a sediment cover.

  2. Experiment to determine soil texture by touch and physical analysis

    the greater percentage at 83.83%m followed by the silt at 13.07%, and finally the clay at 3.10%. In addition, another weighed sample of soil was taken and left to dry in the oven for a period of two days. After the oven dry procedure ended, we could then analyse the

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work