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Demonstration goals:

Understand the impacts of cooling rate on decision sizeUnderstand exactly how rapid cooling can lead to crystal fractionalizationIDEA:

When magma cools, crystals kind because the equipment is super-saturated with respect to some minerals. If the magma cools quickly, the crystals perform not have much time come form, so they are really small. If the magma cools slowly, climate the crystals have enough time to grow and also become large. Part granites contain minerals which are up to one meter (3 ft) across!


Diorite with huge Ca-feldspar crystal

The dimension of crystals in one igneous rock is an important indicator of the conditions where the absent formed. One igneous absent with huge crystals probably shows that the rock created deep within the Earth, due to the fact that it is generally warmer deep within the planet than near the surface. These room called intrusive rocks, and they have a phaneritic texture (from the Greek “phanerous” definition visible). Similarly, a absent with tiny crystals probably created at or near the surface and also cooled quickly. These are called extrusive rocks and have an aphanitic texture (from the Greek “a-” meaning not, and “phanerous”). And also some magma cools so easily that no crystals form; we say the these have a hyaline structure (from the Greek “hyalis” meaning glass).

You are watching: If a crystal cools rapidly it will be


Granite with large K-feldspar crystals

Sometimes, a rock will certainly contain both aphanitic and also phaneritic crystals in it. This method that something important odd happened to the magma before it to be erupted. Because we recognize that big crystals need time come grow, the magma must have spent part time deep underground. Yet the smaller crystals typical that the rest of the cooling happened an extremely quickly. If a rock has both crystal types, it method that the mamga spent some time in a magma chamber, where the large crystals grew, then was violent erupted top top the surface, where the little crystals were formed. A great example the this is the Colbert Rhyolite in the Arbuckle mountains of Oklahoma.

We deserve to simulate the expansion of minerals utilizing some typical materials; just around everyone has grown salt and also sugar crystals indigenous a supersaturated solution. However, those experiments take an ext time 보다 is usually available in the classroom, so we have arisen a demonstration based upon one provided in Jackson, J. H., and also E. D. Evans, 1980, Spaceship Earth: earth Science, modification Edition, house turn Mifflin Company, p. 245-246.

To perform this experiment, you will certainly need:3 Mothballs (napthalene)3 Crayons3 test tubes (50 mL or larger) or 3 little beakers (50 mL or larger)1 big beaker (250 mL or larger) with 100 ml of boil water1 big beaker (250 mL or larger) v 100 ml of warm water1 large beaker (250 mL or larger) with 100 ml of ice cream water1 warm platePair of pliers

Melting the mothballs and also crayon mixture

Cooling the mothballs and also crayon mixture

Before the demonstration:Fill one beaker through 100 mL the water and also place it on the warm plate; lug to a boil.

Crush one of the mothballs through the pliers and place it right into a test tube; to like a crayon and include it to the check tube. Shiver the test tube to mix the mothball and also the crayon. Repeat, placing the various other mothballs and crayons right into separate check tubes. Location all 3 test tubes into the manufacturer of cook water till the mixture melts completely.

Warning! Mothballs and crayons both give off flammable gasses as soon as heated. Do not location the molten mixture near an open up flame or spark!

1. Utilizing tongs, ar one check tube right into the heat water and one into the cold water at the start of class. Begin your lecture on crystal size and also morphology.

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2. After around ten come fifteen minutes (depending on the temperature that the warmth water), remove the check tubes from the beakers. Compare the dimension of the crystals. You may need to use a magnifying glass in stimulate to watch the crystals clearly; rotating the tube (to catch specular reflection) may likewise help.

Do you notice anything unusual around the crystals in the tube which was inserted into cold water? (HINT: Is there a color change from optimal to bottom the the test tube?)

For Discussion:

Why go the crystals grow to various sizes? go crayon color have any kind of effect ~ above the crystal size? What around the loved one amount the mothballs? based upon what you have discovered, deserve to you explain why ice cream must be churned? (Try making ice cream cream without churning!)

This demonstration was adjusted from Jackson, J. H., and also E. D. Evans, 1980, Spaceship Earth: planet Science, modification Edition, house Mifflin Company, p. 245-246