While many stones may have pores with variable sizes, rocks that contain air bubbles generally belong to the extrusive class of Igneous rocks.
Extrusive igneous rocks form when lava erupts onto the surface of volcanoes and rapidly cools to form crystals.
This article will highlight four rocks that contain air bubbles, their physicochemical properties, and where you can find them.
4 Rocks That Contain Air Bubbles
Pumice is a volcanic rock composed of highly vesicular rough textural rock glass.
It is generally light in color. Pumice is the most common rock with air bubbles.
Pumice forms when hot felsic lava collides with water.
This is most common near bodies of water or underwater volcanoes.
When hot magma comes into contact with water, rapid cooling and pressure loss cause bubbles to form and the lava to solidify.
The air bubbles are trapped within the solid rocks that form.
Pumice is an amorphous aluminum silicate composed of 76% silicon dioxide and 13% aluminum oxide.
Pumice is a distinctive rock due to its low density and lightweight.
Pumice, which has a porosity of 64–85% by volume, can float over water until its vesicles are filled, at which point it sinks.
Two types of holes in the rock exist.
Some are tubular, while others are nearly spherical.
This rock comes in many colors, but it is always pale in appearance.
There are a variety of colors available, including white, blue, and gray.
Pumice has a melting point of 900oC, Mohs hardness of 6, and a pH of 7.2.
Rockhounding locations of Pumice
Pumice is found worldwide as a result of continental volcanic eruptions and undersea volcanic eruptions.
Pumice may also be found in locations where there are no volcanoes, since these floating stones can be spread by ocean currents.
If you are an amateur rockhound looking to add pumice to your collection, there are several locations to choose from.
Italy produces the most pumice due to its many erupting volcanoes.
While pumice is found across the United States, famous states with pumice include Nevada, California, Arizona, and Kansas.
In Africa, some pumice deposits have been found in Ethiopia, Kenya, and Tanzania.
Scoria is a dark-colored, air-filled volcanic rock that may or may not include crystals.
The majority of this rock is composed of basaltic or andesitic minerals.
Scoria vesicles arise when gases dissolved in magma come out of solution as it erupts, forming bubbles in the molten rock, some of which are frozen in place as the rock cools and solidifies.
Mafic lava has a lower viscosity than felsic lava.
As a result, trapped air in mafic lava can easily move about, generating larger vesicles than those seen in pumice.
It is made of around 50% silica and 10% calcium oxide, with lower amounts of potash and soda.
Scoria varies from pumice, another vesicular volcanic rock, in that its vesicles are larger and its vesicle walls are thicker.
Scoria has a specific gravity greater than one and hence sinks when submerged in water.
Fresh rock may be pitch black and gleaming. Due to oxidized iron, older material is duller, browner, or even reddish.
Rockhounding locations of Scoria
Tenerife, Spain, and the Canary Islands are scoric havens.
In the United States, rockhounds can also discover scoria in Arizona, Oregon, Hawaii, and New Mexico.
Obsidian is made from high-viscosity felsic lava that is rich in silicon, oxygen, aluminum, sodium, and potassium.
Obsidian is generated from the parent material, which is swiftly cooled lava.
This occurs when the edges of flowing felsic lava cool rapidly, or when lava cools when it comes into contact with water or air.
The cooled lava traps air bubbles within this glass-like rock.
Even though obsidian is typically black in appearance, its composition is very felsic.
Obsidian is composed of SiO2 (silicon dioxide), accounting for at least 70% of its weight.
Obsidian is a smooth glassy volcanic rock with a deep black or blackish green color.
It has a vitreous sheen, a Mohs hardness rating of 5-6, and a specific gravity of 2.4.
Because obsidian is rigid, brittle, and amorphous, it breaks with sharp edges.
Rockhounding locations of Obsidian
Obsidian is found in areas where rhyolitic eruptions have occurred.
It is common in Chile, El Salvador, Greece, and New Zealand, amongst others.
Yellowstone National Park is a great place to look for obsidian. Washington, Arizona, Oregon, and Utah are among the Western US states with obsidian deposits.
Rhyolite forms as a result of explosive volcanic eruptions.
This is because the silica-rich magma produced during these eruptions is so viscous that it does not flow in a river of lava.
Rhyolite appears when gas-filled lava or magma that has been expelled crystallizes.
When this thick lava cools so quickly, gas becomes trapped inside it, resulting in the formation of vugs (gas-filled pockets with rocks).
Rhyolite is a felsic rock with a high silica content of 69 to 77%.
The bulk of its mineral composition is made up of quartz and plagioclase, with minor quantities of orthoclase and biotite.
Rhyolite comes in a variety of light tints.
It can have any texture, from smooth glass to fine-grained rock (aphanitic) to a substance with visible crystals (porphyritic).
The rock’s hardness and toughness vary based on its composition and the initial amount of cooling that generated it.
It has a Mohs hardness scale of 6.
Rockhounding locations of Rhyolite
It is possible to go rockhounding for rhyolite in some regions even as an amateur.
Yellowstone National Park in the United States, Tambora National Park in Indonesia, and Iceland are examples of such places.
Pumice, Scoria, Obsidian, and Rhyolite are four typical rocks that contain air bubbles, and they may be found in a variety of locations.
A variety of distinguishing qualities make it simple for amateur rockhounds to discover and identify these intriguing stones.
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