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Igneous Intrusive Rock

Overview

Source: Laboratory of Alan Lester - University of Colorado Boulder

Igneous rocks are products of the cooling and crystallization of high temperature liquid rock, called magma. Magmatic temperatures typically range from approximately 800 °C to 1,200 °C. Molten rock is, perhaps luckily for humans, an anomaly on planet Earth. If a random and imaginary drill hole were made in the Earth, it would most likely not reach a region of truly and totally molten material until the outer core, at nearly 2,900 km beneath the surface (Earth's radius is 6,370 km). Even there, this molten material would predominantly consist of liquid iron, not true silicate rock, and be incapable of ever reaching Earth's surface.

Volcanic eruptions and igneous rocks do occur though, and they are evidence that there are indeed isolated regions of melting and magma generation within the Earth.

Procedure

1. Grape Juice experiment

Open a canister of store-bought artificial grape juice.
Empty some of the contents into hands and squeeze.
Note that the liquid is a deep purple color, and the remaining solid has lost some of its purple coloration and is now more like clear ice.

2. Cooling Rate and Crystal Size

Sprinkle a layer of thymol crystals in the bottom of a Petri dish, just covering the bottom of the dish.
Set Petri dish on hot plat

Results

1) The grape juice experiment demonstrates the concept of partial melting. Where an initial liquid (melt) is typically of a different composition than the parent rock that undergoes melting.

2) The thymol experiment demonstrates the concept of igneous rock grain size as being related to cooling rate. Rapid cooling generates smaller crystals than slow cooling.

Application and Summary

Igneous rocks are of substantial importance.Geologists identify and map intrusive igneous rocks for a variety of reasons.

Intrusive igneous rocks can be markers of certain kinds of ore deposits. For example, felsic to intermediate composition intrusive magma bodies can act as the heat sources that drive hydrothermal circulation systems, and concomitant precipitation within fractures (veins) of ore minerals including Cu, Mo, Au, Ag, and others. In contrast, mafic to ultramafic intrusions are as