Gem Profile- Basalt

by Judy Ellis

As I said last week, I love the processes of our amazing Earth. This week we're going to talk about a pretty amazing, but really basic rock: Basalt.

If you look at basalt, you won't find much. It's black with no real crystalline structures and hardly any sparkle, dazzle or sheen (unless polished of course). Yet, for all of its boring attributes, the story of basalt is one of fire, floods and excitement...okay, if you like volcanoes like I do, then it's exciting!

How Basalt is Formed

Basalt is the most common rock in Earth's crust.

The seafloor consists mostly of basalt.

It forms as igneous extruded volcanic rock with aphanitic to porphyritic texture.

Composed mainly of plagioclase and pyroxene, it has low silica and low viscosity.

In plain English: Basalt is liquid lava rich in magnesium and iron with low silica.

It cools with barely any visible crystal structure.

Basalt originates at the Mid-Atlantic Ridge, hotspots, shield volcanoes, and other volcanic regions.

We've found it on the moon and Mars.

Polished basalt cabochons and rough lava beads.

Basalt is the most common rock on our planet.

It forms at divergent plate boundaries like the Mid-Atlantic Ridge, splitting the North American and Eurasian plates.

Iceland, the Azores, and Canary Islands lie along this ridge.

Newer rock sits closest to the boundary.

Spreading creates ridges as lava cools.

Magnetite in basalt aligns with magnetic north.

Earth's polarity changes allow us to measure reversals via seafloor spreading.

Basalt also forms from hotspots or magma plumes under ocean crust.

These create shield volcanoes like the Hawaiian and Galapagos Islands.

It builds Olympus Mons, Mars' largest volcano, and the moon's lunar seas.

Glowing molten basalt.

It might be under your feet!

Magma plumes create many basalt flood plains on continents.

A hotspot under Yellowstone National Park has erupted large basalt flows.

The Snake River plain in southern Idaho traces tectonic plate movement across the Yellowstone hotspot.

This plume also formed regional basalt flood plains, including the Columbia River Basalt Plains in Washington and Oregon.

Huge fissures allowed hot lava to flow.

Basalt's low silica lets lava flow up to 15 mph and cover vast areas.

The Columbia River plain flow reaches nearly 6,000 feet deep and covers over 100,000 square miles.

Spokane, Washington, sits on a basalt field. Spokane's famous river runs through the city, with basalt rocks in the water.

The Siberian Traps dwarf other flows.

They erupted lava covering nearly 37 million square miles.

Scientists link them to the dinosaurs' demise.

Flood plains like these exist worldwide in smaller quantities.

Basalt also forms dikes, sills, and columns that puzzled early geologists.

Ireland's Giant's Causeway features basalt columns from cooling and shrinking.

They create geometric shapes from above.

Devil's Tower in Wyoming shows columnar jointing from a cooled basalt volcano, with erosion exposing the hard core.

The Devil's Postpile near Mammoth Lakes, California, and Paul Bunyan's Woodpile in central Utah offer more examples.

Devil's Tower in Wyoming.

Depending on where you live, people say buh-SALT or BAA-salt.

Either way, it is hardened lava.

It can resemble charcoal pellets.

It can also host amethyst or other gems inside.

Basalt has a hardness of 8 on Mohs scale.

It takes a nice polish but looks beautiful unpolished too.

The process to see and use this plain black rock is fascinating!

Non-Jewelry Basalt Uses

Basalt stones aid massage therapy to alleviate stress.

They're thought to rid the body of anger.

They also help understand others' points of view.

Basalt promotes reproductive health, stability, and clarity.

During difficult times, basalt helps draw on your inner "fire" and diminish negative influences.

Gem Profile- Basalt

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