We know three main classes of rocks, sedimentary, igneous, and metamorphic. In Limestone article, we learned how sedimentation occurs, and the formation of sedimentary rocks takes place. Today, we are going to know Obsidian rock, which falls in the main class igneous rocks.

We know igneous rocks have two basic types:

1. Intrusive Igneous Rocks

When molten lava/magma is cooling slowly below the surface of the earth and forms large crystals in the rocks they known as intrusive igneous rocks. For examples-

Diorite
Diorite
Gabbro
Gabbro
Granite
Granite
Pegmatite
Pegmatite
Peridotite
Peridotite

 

1 – Extrusive Igneous Rocks

When molten magma is cooling rapidly onto the surface of the earth and forms small crystals in the rocks they known as extrusive igneous rocks. For examples-

Obsidian
Obsidian
Andesite
Andesite
Basalt
Basalt
Dacite
Dacite
Pumice
Pumice
Rhyolite
Rhyolite
Scoria
Scoria
Tuff
Tuff
Fire Opal
Fire Opal

 

What Is Obsidian Rock?

If you strive to know the obsidian meaning, go ahead in this section. Obsidian is a class of igneous rocks, which forms when felsic lava extruded from a volcano onto the surface of the earth.

The cooling of lava takes place so rapidly that no chance remains for proper crystallization (Atomic Arrangements) and finds as an amorphous glass material. It has a smooth and uniform texture, which breaks with a conchoidal fracture.

Geological Classification of Obsidian Rocks:

Let’s see the classification of obsidian rocks at the perspectives of a geologist.

Class: Igneous Rocks

Sub-Class: Medium Hardness Rocks

Family-Group: Volcanic

Category: Opaque Rocks

Alternate Names: Lava, Glassy Lava, Xaga, Royal Agate, Glass Agate, Volcanic Glass, Glass Gem, Guardian Gem, and Black Beauty

 

Formation of Obsidian Rocks in Nature

We have seen in the earlier section that obsidian is an extrusive rock type and formation used to takes place on the surface of the earth when magma or lava coming out due to volcanic phenomena and rapid cooling takes place. The obsidian formation can happen in a variety of cooling environment such as

  • Along the edges of a flow of magma or lava
  • Along the edges of a dome of the volcano
  • Along the edges of a sill or dike, which takes place under the surface and it is the only intrusive type
  • The point where magma comes into the contact of water on the surface
  • The point where magma cools due to airborne cooling effects

 

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Properties of Obsidian

Obsidians have various physical & visual properties, such as Hardness, Grain Size, Fracture, Streak (Colors), Porosity, Luster, and Strength. These all property attributes determine the applications of obsidian rocks. Let’s see some significant properties of obsidians.

Streaks & Colors of Obsidian

The streak of obsidian is white, but various colors occur in nature.

Frequently found colors of Obsidian rocks are:

The highest occurrence of obsidians is in Black, but it also available in Brown, Green, or Tan.

Rarely found colors of Obsidian rocks are:

A very rare occurrence of obsidians is in Blue, Orange, Red, and Yellow.

The occurrence of color is due to the presence of different trace elements in obsidian rocks.

 Streaks & Colors of Obsidian
 The hardness of Obsidian

The hardness of Obsidian (How Hard Is Obsidian Rocks)

In physics and geology, the hardness of the physical objects or rocks is measured in Moh’s scale, which rates the objects in question on the scale from 1 to 10.

  • Rocks with Moh’s hardness scale from 1 to 3 are considering soft rocks.
  • From 3 to 6 scale – medium hardness
  • From 6 to 10 hardness scale – the hardest rocks

Based on the Moh’s hardness scale, obsidians fall into a medium hard category of rocks because obsidian rocks have 5-5.5 Moh’s hardness scale. It also means obsidian is easy to scratch.

Compressive Strength of Obsidian

When a compressive pressure (In Newton unit) applied on the rocks a permanent deformation of rocks takes place at a point of pressure. It is termed as the compressive strength of rocks and obsidians fractured or permanently deformed at 0.15 N per square millimeter. It means obsidian is easy to break and chipped by some impacts. It also renders obsidian as the unfit stone for rings and bracelets like jewelry production.

Porosity of Obsidian

It is a less porous rock, so it has medium hardness.

Obsidian Fracture

Obsidians breaks into the conchoidal fracture. Obsidian has no natural or defined planes of separation when a pressure exceeding from its physical strength exerts on it. Therefore, smoothly curved fracture takes place on the surface of obsidian glass rock.

The images at the side are depicting the phenomena beautifully and precisely.

 Compressive Strength of Obsidian
 Porosity of Obsidian
 Obsidian Fracture

Specific Gravity & Density of Obsidian

The density of rock used to expresses as specific gravity, and it is measured in relevance to the density of water in gram per cubic centimeter of the mass. The density of obsidian is 2.55 g/cubic cm. It means it is heavier than water and dense medium as a mass.

Luster & Transparency of Obsidian

In Obsidian, only 1% of water exists. It means it is vitreous and due to the high presence of silica and other glass-forming minerals, it is translucent in transparency.

Specific Heat Capacity of Obsidian

We usually measure the specific heat capacity of solid in the amount of heat energy (In Jules) required to increase the one-degree centigrade temperature of a unit mass of the substance. Thus, obsidian has 0.92 KJ per Kg K. it means it is a heat resistant rock and cannot molt at low temperature when treated with heat energy.

 

What Type of Rock Is Obsidian?

Geologically, rocks used to divide into types. Based on the texture of the Obsidian rocks types are decided. The main types of Obsidian rocks are as follows:

Mahogany ObsidianMahogany Obsidian When two colors, Black and Brown swirled together in a single obsidian rock, Mahogany Obsidian takes place.
Obsidian is kind of glass and chemically unstable. Overtime crystallization process takes place in the mass of rock. If the formation of crystals happens in a radial cluster of white or gray crystals (cristobalite) at different and isolated locations, it referred to as Snowflake obsidian. Snowflake ObsidianSnowflake Obsidian
Rainbow ObsidianRainbow Obsidian Seldom obsidians have an iridescent or metallic “Sheen” thanks to the reflection of light rays. It used to takes place due to minute inclusions of mineral crystals, gas trapped in obsidian, and some debris. It results in a prismatic effect found due to glass matter of obsidians, and white light rays are fragmenting in the rainbow color spectrum.
If metallic sheen reflecting light rays in golden color, the gold sheen obsidians occur. In black obsidian, golden inclusions take place it shines as yellow and honey metals in the mass of obsidian. Gold Sheen ObsidianGold Sheen Obsidian
Silver Sheen ObsidianSilver Sheen Obsidian Similarly, if metallic sheen found in silver color, the silver sheen obsidians take place.
When tiny bubbles of gas trapped in the rock and resulting in reflection of purple color, a purple sheen obsidian happens. Purple Sheen ObsidianPurple Sheen Obsidian
Double Flow ObsidianDouble Flow Obsidian Sometimes the two different colors exist in the same specimen of the obsidian rock. Moreover, the occurrence of different colors takes place in a pattern of flows, and it is flowing in a different direction, we termed it a double flow obsidian.
Black is the most common color found in obsidians. Therefore, the highest occurrence of obsidians found in the black glass. It projects shiny black hue and popular as a black gemstone in the jewelry industry. Black ObsidianBlack Obsidian
Pumpkin ObsidianPumpkin Obsidian When obsidian is reflecting mainly pumpkin color in pale brown shades, it called as pumpkin obsidian. It resembles Mahogany obsidians in looks and brown to black and beige bands of colors found in the mass of obsidians.
Green colored obsidians occur seldom and when polished they resemble emerald and used in jewelry purposes. It found in mossy to pickle green color shades. Green ObsidianGreen Obsidian

 

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The occurrence of Obsidian Rocks in Different Geographic Regions of the Earth

Obsidian is falling into a volcanic-group of rocks. Therefore, the occurrence of Obsidian confined to geological areas where volcanic activity happened in the recent past. Obsidian rocks are not expected in volcanic areas of distance past like before billions of years because the glassy rocks are destroying rapidly due to weathering effects and various geological processes.

Significant deposits of obsidian rocks exist in following continents of the world.

Asia: Afghanistan, Indonesia, Japan, Armenia, Azerbaijan, and Russia.
Africa: Kenya.
Europe: Greece, Hungary, Iceland, Italy, Scotland, and Turkey.
North America: Canada, Mexico, and USA.
Central America: El Salvador, Guatemala, and Papua New Guinea.
>South America: Argentina, Chile, Ecuador, and Peru.
Australia: New Zealand.

 

The highest production of jewelry grade obsidians takes place in the United States. However, in the USA, obsidian rocks are not found in eastern regions of the Mississippi River because that area lacks volcanic activities in the recent past at all. The remaining areas of the States of America where obsidian rocks available are:

Arizona California Idaho Nevada
New Mexico Oregon Washington Wyoming
Colorado Texas Utah

 

Obsidian rocks also available in Virginia, Pennsylvania, and North Carolina.

Obsidian Uses

Now, I am going to acknowledge your use of obsidian. Do you know conchoidal fracture of a rock resulting into pieces of rocks in curved surfaces?

Obsidian rocks can produce fragments with sharp edges, and sharp fragments of obsidian rocks first used as cutting tools in ancient eras of the civilization of humankind.

Today, a variety of uses found in different industries, such as:

Obsidians as Weapons & Tools:

The human civilization has used obsidian rocks to make knives, spear points, arrowheads, scrapers, and various weapons.

Knives and blades were fine for kitchen applications. Scrappers were used in land digging, agriculture, and gardening applications. Arrowheads and spear points were provided the sharpest tools for warriors in the creation of various weapons.

 Obsidians as Weapons & Tools
 Obsidians in Construction Industry

Obsidians in Construction Industry:

Obsidian rocks use in interior and exterior decoration. Decorative aggregates, gravels, and pebbles from obsidian rocks are a favorite material for creating architectural beauty and artwork on walls, ceilings, and floors of the buildings. Artworks in gardens, patios, swimming pools, fire features, and water features look amazing when obsidian rocks applied along with other Gemstones.

It also used as mirror elements in the decoration of the interior, exterior, and construction of artifacts for various applications in life.

Obsidians in Medical Surgery:

Obsidian rocks are continuously used in the modern era to create cutting-edge surgical tools. Studies have revealed the fact that thin blades for scalpel of obsidians are superior in sharpness and performance than or equivalent to blades created from the latest surgical steel.

Do you know household razor blades are 300-600 Angstroms while obsidian can produce blades of 30 Angstroms? It means obsidian can produce the sharpest materials that only Nanotechnologies can produce.

If you look at the sharpest edge of the steel blade in the microscope, you will notice almost saw-like teeth on edge. Whereas, the obsidian blade has no bite because it has evenly sooth edge at the microscopic level. Therefore, wounds cut by obsidian blades are healing significantly faster than wounds by steel blades.

 Obsidians in Medical Surgery
 Obsidians in Antiquity and Jewelry Industry

Obsidians in Antiquity and Jewelry Industry:

Obsidian rocks often cut into beads and cabochons. Mahogany and Snowflakes obsidian types of rocks are providing gemstones for earrings, brooches, and pendants.

In the creation of Opal Doublets and Triplets, a thin slice of obsidian is glued as a backing material in the construction of composite gemstones. The black obsidian is an ideal material in making Opals to offer color-contrasting background.

However, medium strength of obsidian with 5.5 hardness creates durability concerns and the jewelry industry avoid its use as they apply diamonds and other gemstones.

 Obsidians Jewelry

 

Obsidian Rocks for Sales

If you are curious about obsidian for sale, I would like to describe obsidian rocks for sale in a nutshell here.

Obsidians are delicate rocks for many jewelry applications where chances of various impacts are high. So, the jewelry industry avoids the high usage of these natural rocks/gems/glasses. It mainly used in delicate jewelry, and the following varieties are popular for commercial usages of obsidians.

The richest market of obsidian for sales is aiming for heal purposes. It is believed that obsidian stones have natural healing capabilities. Therefore, along with described various obsidian types earlier, following varieties of obsidian products are in demand in the healing gemstone market.

Apache Tears
Apache Tears
Spiderweb
Spiderweb
Cat Eye
Cat Eye
FlameFire
Flame/Fire
Peanut
Peanut
Midnight Lace
Midnight Lace

 

eBay and Etsy are popular marketplaces to obtain raw obsidians. Various ecommerce jewelry sites are selling ready to use jewelry made from different kinds of obsidian rocks and for a variety of jewelry products. The online marketplaces including Alibaba and others are selling sorted and unsorted rough obsidian natural stones are weighing from 1/4lb to 1-2lbs.

Wrapping It Up

In the series of identifying various rocks and natural stones at World of Stones, USA, we have explored different aspects of obsidian rocks such as meaning, uses, facts, properties, and colors of obsidians.

World of Stones, USA is an excellent place to buy a variety of natural rocks mainly used for exterior applications in building construction industry. If you are interested to know about rocks and stones, keep the reading of blogs at World of Stones.

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