Obsidian is felsic because it is formed when felsic lava from a volcano rapidly cools with limited crystal growth.
Obsidian basically consists of at least 70% silicon dioxide.
Although obsidian is black-colored, it is very rich in silica and lacks crystals-which means it is lacking in minerals, thus making it a natural glass.
In this article, we will explore all you need to know about Obsidian and answer all related questions.
Is Obsidian Felsic or Mafic? (Explained)
What exactly is Obsidian?
Obsidian is an igneous rock that occurs as a natural glass and it is formed through the cooling of viscous lava from active volcanoes.
Furthermore, obsidian has abundant silica content measuring between 65 and 80 percent.
The mineral has a close chemical similarity to rhyolite and is low in water composition.
Although Obsidian has a jet-black coloration, the presence of hematite creates brown and red varieties, while the presence of small gas bubbles may lead to a golden sheen.
Obsidian is categorized as moderately hard and has a smooth and curved fractured surface while also having sharp edges.
Freshly broken obsidian boasts one of the sharpest known edges of any man-made or natural material.
Obsidian has been used over time for making implements, weapons, tools, mirrors, and ornaments.
Due to the mineral’s conchoidal fracture, most of the very sharp stone artifacts were carved from obsidian.
Furthermore, felsic igneous rocks are made up of at least 75 percent felsic minerals which have a very high silica content.
Felsic minerals generally include oxygen, silicon, sodium, potassium, calcium, and aluminum.
What makes a substance mafic or felsic?
The term mafic is used to describe magmas, silicate minerals, and rocks that have high heavier element content.
Mafic magmas are quite rich in sodium and calcium and the minerals are known to have specific gravities greater than 3.0.
Some very common rock-forming mafics include pyroxene, olivine, amphibole, biotite mica as well as plagioclase feldspars.
Some common mafic rocks include gabbro and basalt.
On the other hand, felsic is a term used in describing magmas, silicate minerals, and rocks that have a lower constitution of heavier elements.
Felsics have high light element constituents such as aluminum, silicon, and potassium.
The term felsic is derived from SIC, which indicates a high percentage of silica and FEL, which stands for high feldspar content.
Felsic minerals have a light coloration and feature a specific gravity that is lower than 3.0.
Some common felsic minerals include muscovite mica, quartz, and orthoclase feldspars.
Granite ranks as the most common among felsic rocks.
In summary, felsic is located mostly in convergent zones while mafic lava is commonly found in mid-ocean ridges.
Also, felsic lava is less viscous than mafic lava and mafic lava flows easily, while the felsic lava soon becomes stuck, and mafic is less susceptible to explosions.
Additionally, mafic lava is capable of creating basalt while felsic lava creates rhyolite rocks and andesitic.
What makes obsidian Felsic?
Obsidian is a volcanic glass that formed from the eruption of felsic lavas which has the unique feature of having heavy concentrations of silica.
Due to their high silica composition, felsic lavas don’t act like silica-poor or mafic lavas.
Although obsidian has a dark color just like mafic rocks, the composition of obsidian is largely felsic.
This mineral is made up of SiO2 with a base composition of 70%.
Some crystalline rocks that have an obsidian composition include rhyolite and granite.
Why should you know about obsidian’s felsic origin?
Some petrographic features of the natural state of obsidian include sharp edges, a dark color, and pronounced conchoidal fractures.
Also, obsidian doesn’t have any macroscopically identifiable inclusions of liquids, gases, or solids like rock fragments.
Obsidian doesn’t scratch glass and, as such, has a hardness of 5 or 6 according to the Mohs scale.
The mineral is translucent with sharp margins and thin cleavage fragments.
Felsic rocks such as obsidian can be easily identified by their texture, color, and other physical attributes.
Many of the felsic rocks out there are light-colored but they usually have varying textures.
Also, some felsic rocks like granite are generally of coarse texture, while the likes of rhyolite have fine grains.
Furthermore, felsic rocks are known to have glassy textures just as they are in porcellanitic and obsidian.
Knowing the features of felsic minerals makes it easy to identify the exact mineral it is.
Obsidian is an igneous rock that is composed of magmatic content which is largely encrypted.
Most of the rock is not crystallized, largely because its crystals face two distinct challenges to their growth.
Obsidian can be found in places rich in rhyolitic temperatures, such as Australia, Argentina, and Chile.
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