What is a Photomicrograph?

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Depending on the context and structure being examined, a photomicrograph is a representation of a person or scene in the form of a print or transparent slide; recorded by a camera on light-sensitive material.

At a basic level, photo-microscopy may be carried out simply by attaching a regular camera to a microscope; therefore, enabling the user to take photographs at reasonably high magnification.

This type of photography is used to look into the structual form of different types of rocks, and by doing this, we are able to see the ratios of minerals present.

What is an Igneous Rock?

Most rocks are aggregates of crystals or grains of one or more minerals. The minerals that make up the structure of the rock are quite small, although they are still able to be identified.

Ever since the beginning of the Earth, rocks have been the eyes and ears of evolution. Their experiences have been solidly held in a tight capsule, only to be later examined by geologists and researchers.

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One of the most fascinating of all rock forms is unquestionably igneous rocks. Igneous rocks are formed by volcanic eruptions from magma. The molten rock rises to the top of the volcano and either flows down the side of the volcano as lava or aggressively burst’s due to bubble formation in the lava.

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With the help of the bubbles, the magma volume increases even more, shooting out and over the entire surface of the volcano. The rocks that initially hit the surface and cool are called extrusive, meaning they cool at a faster pace because of their direct contact with weathering elements like rain, air, and snow.

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In some cases, the magma will never reach the surface resulting in an intrusive igneous rock. The rocks cool slowly allowing the rock to form crystals that are visible with the naked eye.

For centuries, igneous rocks have been studied because of their ability to share secrets about our planet. They have given scientists, geologists, and researchers the ability to understand volcanic eruptions and when the next eruption will occur. In addition, they make up the majority of Earth’s crust; therefore, they help in understanding our planet and why it differs so much with the entire solar system.

In the larger sense, the Earth’s changes over the years have been widely studied by igneous rocks. While shifts of tectonic plates have formed continents, the remnants left over are igneous rocks.

While all igneous rocks cool from the same magma and form under different conditions, they all display different characteristics of texture, color, mineral composition, and appearance.

Obsidian

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Rainbow Obsidian

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Snowflake Obsidian

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Obsidian is one of the easiest igneous rocks to identify because of the color and glossy appearance. The sharp conchoidal fractures create razor like edges much like a piece of metal. Native Indians used obsidian for arrow heads and knives because of the strong structural form. Obsidian is also used in several different types of eye surgeries because of the tissue compatibility.

Gabbro

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Gabbro is a fine grained rock that is typically composed of black pyroxene and calcium plagioclase. The striations in Gabbro are easily identified on the elongated crystals. The colors in the plagioclase cause a pale blue iridescent glow making this type of rock highly valued in architecture.

Peridotite

 

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Peridotite is typically made up of olivine and pyroxene which gives it the dark green to dark gray coloring. The crystals in the Peridotite can be of any size depending on the cooling times and the ratios of minerals. Peridotite is not abundant in Earth’s crust; however, it is the most abundant rock beneath the crust in the upper mantle.

Rhyolite

 

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Rhyolite is a fine grained extrusive igneous rock that can be found in many varieties of color and shape. There particular form, which typically is porphyritic, is identifiable by the glassy quartz crystals with the addition of the potassium feldspar phenocrysts. If there are no phenocrysts present, a lighter color sometimes suggests this particular type of igneous rock. However, the simple act of testing the hardness, texture, fractures, and cleavage will lead a researcher to the correct identity.

Andesite

 

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Andesite is typically found at convergent boundaries where volcanos are formed. They are gray in color and possess phenocrysts of white to light gray plagioclase and black hornblende.

Granite

 

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Found at Yosemite National Park

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Source (Orbicular granite in Caldera, Chile)

Source (The granite peaks of the Torres del Paine in the Chilean Patagonia)

Granite is quite familiar to many being that it’s typically used to construct monuments, flooring, walls, pillars, and many other structures. Granite makes up the large grouping of intrusive rocks called batholiths, ranging in colors from light pink, dark and light grays to reddish tones. The essential mineral in granite is potassium feldspar, which gives it the luminous and glossy like finish when polished.

Unique forms of granite will have traces of hornblende and biotite, which gives the rock a rich and lavish appearance and a black hue.

Pumice

 

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Familiar to most as a normal pumice stone, its structure is the result of the frothing of volcanic glass. The color is typically white or gray and the texture is abrasive, which explains its use in homemade spa products for the skin. You can also find pumice is lava soap, which is used my many for a more industrial like cleaning.

Basalt

 

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Basalt is probably the most identifiable and abundant of all igneous rocks, forming the base of the ocean floor and large land structures. Basalt will have phenocrysts of calcium plagioclase, combined with some smaller olivine crystals measuring 1 mm, recognizable by their greenish hue and glassy sheen.

Bowens Reaction Series

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 The study of igneous rocks was summed up by the Bowens reaction series, which explained the sequence of steps the magma takes to become a crystallized form.

In the 20th century, Bowen duplicated the crystallization process in the lab where he paid close attention to the reactions specific to each mineral. He coined the phrase “discontinuous reaction”, which was an experiment in the cooling times of magma and which minerals were present at the end of the process.

Consequently, he also coined the phrase “continuous reaction”, resulting from an experiment using plagioclase feldspars which change in composition as the magma temperature decreases.

To put it simply, Bowen’s series of reactions shows that when magma cools, certain minerals will crystallize more quickly than others. There is a sequence present to the cooling process in which “olivine and plagioclase ranks higher on the list, crystallizing at temperatures of 500° to 600°C.”

The Bowens reaction series is not an exact science being that composition and instruction can influence the outcome. The series was meant to explain the common order of crystallization, while allowing for a certain margin of error.

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