Question 1         What mineral was mined in a pegmatite near Wickenburg, AZ?           Answers: Silver   Gold     Lepidolite   Peridot       Question 2         How do the crystals in pegmatites get so large?           Answers: It is a matter of time

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Silver

Gold

Lepidolite

Peridot

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It is a matter of time. The longer the crystal grows the bigger the crystals become. In pegmatites the crystals grow for 10's of billions of years.

They grow in solutions rather than in melts. This allows the ions to move around easily and add the necessary nutrients to the growing crystals.

Pegmatite crystals grow at the expense of smaller ones. In the igneous environment the associated heat caused small crystals to merge into larger ones. It has to do with what is known as the "free energy" at the surface of the crystal.

Because pegmatites grow only deep beneath the surface of the Earth, no one has ever seen they grow. Their large size is still a puzzle to science.

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in the upper mantle.

near the inner core of the Earth

when sea water mixes with magma, as in the Hawaiian volcanics.

in space, from asteroids

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Abrasives like sandpaper.

Paint pigments

Gemstones

Lasers

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Turquoise

Labradorite

Azurite

Olivine

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Granite has quartz while the diorite does not.

The crystal size. Diorites form deeper within the Earth and thus have larger crystals.

Granites have more feldspars that diorites.

Diorites are dominated by metallic minerals that give an overall bright sheen to the rock.

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Any coarse grained igneous rock.

An igneous rock that can take a high polish.

An igneous rocks that is dominated by phenocrysts.

An igneous rock that contains both light and dark colored crystals.

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Granite

Rhyolite

Apache Tears

Volcanic agglomerate

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Apache Tears grew in the volcanic rock as it slowly cooled after the eruption.

They are the remnants of a devitrification process of obsidian. As the obsidian changes from a glass to perlite, small areas of obsidian are left. These are the Apache Tears.

The Apache Tears are small pieces of obsidian that were fired into the air during the volcanic eruption. The tears fell to the ground and were incorporated into the volcanic dust as it solidified.

Apache Tears are xenoliths. They were formed at an earlier stage of the volcanic eruption and were included in the new lava.

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Quartz

Mica

Glass

Feldspar

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It has many pore spaces full of air that are not interconnected. This make pumice less dense than water.

Pumice strengthens the surface tension of the water. As a result the water tends to "exclude" the pumice and it forces the pumice to the surface... it floats.

Pumice is made entirely of very light weight minerals that contain H and He. The overall density is less than that of water so it floats.

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When the very fluid lava flows of the Hawaiian volcanics meet the sea they cool quickly. The rapid cooling produces short crystals that stick up above the lava. The crystals look like hair.

Pele's Hair is formed thousands of feet above the volcano. In this area an abundance of volcanic gases along with dust and ash, begin to combine in long fibers. When the fibers are big enough they fall to the ground as Pele's Hair.

In Hawaii the very fluid basaltic lava flows have gas bubbles. When the gas bubbles erupt at the surface they send a streamer of glass into the air. These glass strands are Pele's Hair.

As the lava cools, tiny openings on the surface of the lava are formed. From these openings jets of hot gas emerge (fumaroles). Long slender crystals of sulfur, biotite and plagioclase form from the gases. These crystals look like hair.

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The process that causes obsidian to darken is related to ozone in the atmosphere. With a thinning of the ozone more ultraviolet light makes it to the surface of the Earth. This radiation darkens the obsidian.

Initially the obsidian is clear but quickly oxidizes upon contact with the air.

An abundance of iron and magnesium creates the dark color.

When the obsidian is erupted from the volcano it is very hot and caused the surrounding vegetation to burn. The smoke and charred plant fragments give it its dark color.

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As the obsidian slowly cooled the magnetic field of the Earth caused the iron rich minerals in the obsidian to line up. This alignment is what causes the sheen.

The sheen is produced by microscopic fractures in the obsidian that reflect the light.

Microscopic bubbles that are aligned.

Tiny crystals of quartz trapped in the obsidian.

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Scoria is a variety of basalt. The scoria contains many gas pockets.

Scoria contains phenocrysts while basalt does not.

Scoria is an exceptionally red volcanic rock formed by lavas with a very high temperature.

Basalt is iron rich while scoria is iron poor.

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It refers to a volcano that did not explode as expected. It is used by volcanologists who were expecting a much more energetic explosion, as in the expression, that volcano bombed.

It is a term that refers to the explosive nature of some volcanoes, especially those that have excess gas.

A streamlined fragment of volcanic ejecta.

It is a volcanic rock that contains a great deal of volcanic gases. If it is disturbed it could explode.

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A rhyolitic basalt

Amygdaloidal

Stretched basalt

Nutty

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Basalt

Granite

Rhyolite

Obsidian

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It is a term used to describe the origins of a magma.

Phenocrysts are the smallest crystals that make up an extrusive igneous rock.

These are just any large crystal in an igneous rock.

It is the larger crystals in a porphyry.

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The term porphyry refers to an igneous rock that contains both mafic and felsic components. This is a rock that has a distinct "salt and pepper" appearance.

It is any rock that was at anytime in its history, fluid.

It is an igneous rock that contains rocks that were formed somewhere else. These rocks were trapped in the magma as it solidified.

It is a rock that contains two distinctly different sized crystals. They were formed by different cooling stages.

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Andesite

Granite

Felsite

Gabbro

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Topaz

Quartz

Mica

Gold

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Because rhyolite is extrusive, the rock bleaches out in the sunlight over a period of years.

It contains an abundance of silica, sodium, and potassium. These elements produce light colored minerals.

Exposure at the Earth's surface oxidizes the minerals in the rhyolite giving it its light color.

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to flow

felsic

light colored

volcanic

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Visual acuity. If you can see the crystals with the unaided eye it is considered intrusive.

The color of the rocks. Intrusive rocks are generally much darker in color than the extrusive rocks.

Their composition. Extrusive igneous rocks are richer in Si, Al, K and Na.

Xenoliths, if an igneous rocks contains xenoliths it is considered to be intrusive.

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The composition of the melt.

The number of seed crystals that were in the melt.

The length of time it takes for the melt to solidify.

The temperature of the melt.