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Black, Lustrous, Beautiful
Obsidian and Apache Tears make awesome tumbled stones. When tumbled properly they are jet black, highly lustrous and beautiful. Many of them are also transparent. However, some people have a hard time tumbling these natural glasses because they often bruise or chip in the tumbler. However, you can easily get super results by tumbling them gently in a generous amount of reusable ceramic media. We describe the process and a few tips that will help ensure your success.
Tip #1: These materials are soft. They have a Mohs hardness of about 5. Because they are soft, they shape quickly in a tumbler barrel with silicon carbide grit. We skip the coarse grit step and use a three step tumbling process - 1) medium grit; 2) fine grit; and, 3) polish.
Tip #2: These materials are fragile. The particle-to-particle impacts within the tumbler are what cause bruising and chipping. When we tumble them we always surround them with small cylinder-shaped ceramic media. We fill the tumbler barrel with about 50% ceramic media and about 50% obsidian/Apache tears. The ceramic cylinders act like roller bearings and promote a smooth tumbling action. They prevent the pieces of natural glass from hammering against one another in both rotary and vibratory tumblers. Without the cylinders, the pieces of glass will likely be cracked, broken or chipped around the edges.
Tip #3: These materials can produce gas in the tumbler barrel. You read that right. Small amounts of gas are produced as these materials are worn away in the tumbler. This only causes a problem when your tumbler barrel has a lid that can be pushed off by a small amount of gas pressure in the barrel. If you have a vibratory tumbler this is not a problem. Take care of the gas by 'burping your barrel' if it starts to bloat. Or, you can follow the advice given by Steve Hart, author of the book 'Modern Rock Tumbling' - he adds 1/2 teaspoon of baking soda to the tumbler barrel to prevent gas production. If you want more information on this read our article: Gas in the Rock Tumbler Barrel?
Tumbling Recipe: Apache Tears or Obsidian in a ROTARY Tumbler
Barrel Loading: Fill the barrel 2/3 full with 50% Apache Tears and 50% small ceramics.
Step 1: Two tablespoons medium grit (150/220) per pound of rock and ceramics, enough water to cover the rocks. For tumbling whole Apache tears, run four or five days. For broken pieces of obsidian tumble for seven days and inspect. Tumble longer if needed.
Step 2: Two Tablespoons of fine grit (500 or 600) per pound of rock and ceramics, enough water to cover the rocks, tumble for four or five days.
Step 3: Two tablespoons of TXP or #61 Rapid Polish per pound of rock and ceramic, enough water to cover the rocks, tumble for seven days.
Burnish in soapy water for 30 minutes - only if needed. Learn more about burnishing here.
Tumbling Recipe: Apache Tears or Obsidian - VIBRATORY Tumbler
Barrel Loading: Fill the barrel to manufacturers suggested level with 50% Apache Tears and 50% small ceramics.
Step 1: One-half tablespoon of medium grit (150/220) per pound of rock and ceramics, add just enough water to make the grit stick to the rock and media. Run for two days, inspecting frequently to maintain a thin mud slurry. Rinse and inspect your rough after two days. If more time is needed, run for two additional days. Continue until you are satisfied with the shape.
Step 2: One-half tablespoon of fine grit (500 or 600) per pound of rock, add just enough water to make the grit stick to the rock and media, tumble for two days.
Rough Obsidian From Mexico
Step 3: One-half tablespoon of TXP or #61 Rapid Polish per pound of rocks, add just enough water to make a thin polish slurry, tumble for two days. Tumble longer if needed. Don't over tumble.
Burnish in soapy water for 30 minutes - only if needed. Learn more about burnishing here.
Happy Tumbling!
RockTumbler.com Authors
| Hobart M. King has decades of rock tumbling experience and writes most of the articles on RockTumbler.com. He has a PhD in geology and is a GIA graduate gemologist. He also writes the articles about rocks, minerals and gems on Geology.com. |
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 of 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 | Gabbro | Granite |
| Pegmatite | 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 | Andesite | Basalt |
| Dacite | Pumice | Rhyolite |
| Scoria | Tuff | 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 RocksSub-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 contact with water on the surface
- The point where magma cools due to airborne cooling effects
Natural Stone Pavers Collection | ||
Exotic Collection | Premia Collection | Porcelain Pavers |
Steps Stones | Window Sills | Pool Copings |
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.
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.
Streaks & Colors of ObsidianThe 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. | 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.
Based on 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 ObsidianWhen 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 ObsidianIt is a less porous rock, so it has a medium hardness. |
Obsidian FractureObsidians breaks into the conchoidal fracture. Obsidian has no natural or defined planes of separation when a pressure exceeding 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. | Luster & Transparency of ObsidianIn 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. |
What Type of Rock Is Obsidian?
Geologically, rocks used to divide into types. Based on the texture of the Obsidian rock types are decided. The main types of Obsidian rocks are as follows:
| Mahogany 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 Obsidian |
| Rainbow 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 the 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 Obsidian |
| Silver 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 a reflection of purple color, a purple sheen obsidian happens. | Purple Sheen Obsidian |
| Double 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 a shiny black hue and popular as a black gemstone in the jewelry industry. | Black Obsidian |
| Pumpkin 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 for jewelry purposes. It found in mossy to pickle green color shades. | Green Obsidian |
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 the 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 the 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 a conchoidal fracture of a rock resulting in pieces of rocks in curved surfaces?
Obsidian Rough Stones
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 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 the edge. Whereas, the obsidian blade has no bite because it has an evenly smooth edge at the microscopic level. Therefore, wounds cut by obsidian blades are healing significantly faster than wounds by steel blades. |
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 avoids its use as they apply diamonds and other gemstones. |
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 the 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, the following varieties of obsidian products are in demand in the healing gemstone market.
| Apache Tears | Spiderweb | Cat Eye |
| Flame/Fire | Peanut | 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
Raw Obsidian Stone
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 the building construction industry. If you are interested to know about rocks and stones, keep reading blogs at World of Stones.