What Are Those Green Gems in Kilauea's Lava?

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Olivine rocks are common in Hawaii, like these found on Papakōlea Beach. Wilson44691/Wikimedia Commons

Kilauea has been erupting for five weeks, forcing evacuations and evaporating Hawaii's largest freshwater lake in a matter of hours.

Now residents are reporting a new side effect from the volcano: Small green rocks falling from the sky and appearing near lava flows.

It may sound odd, but it's just nature at work.

More olivine please!

"It's literally raining gems," Erin Jordan, a meteorologist based out of Tuscon, Arizona tweeted. The photos in the tweet were sent to her from friends in Hawaii, explaining that they woke up to find small green rocks all over the ground.

Those small green rocks are actually part of the rock-forming mineral group olivine, though you may recognize it more by its gemstone, peridot.

"The lava that is erupting now is very crystal-rich and it is quite possible that residents might be finding olivine," Cheryl Gansecki, a geologist at the University of Hawaii-Hilo who studies the composition of Kilauea's lava, told Mashable.

More like flowing out than raining down

However, several geologists said not to get too excited about these gemstones raining down from up above. They say the gems are rooted inside lava that flows out of fissures around Kilauea and aren't technically falling from the sky. University of Hawaii geologist Cheryl Gansecki said the olivine that people have found could even be from older lava flows, reports CBS News.

"There's not olivine raining from the sky, except in clumps of lava," Gansecki said. "I think this is pretty much a nonstory, unfortunately. What we're seeing are tiny and they do no separate from the lava themselves. You'd have to crush the lava to get them out and find them."

What is olivine?

Olivine is commonly found in Hawaii, which is a volcanic archipelago. Olivine is a magnesium iron silicate, or rock-forming mineral, and is often seen in igneous rock. For those who may not remember science class, igneous rocks are formed by the cooling and firming of magma or lava. Thus, olivine is found in plenty of rocks around Hawaii and is also in the state's roads. In fact, it's possible to go to Papakōlea Beach in Hawaii to experience one of the few green sand beaches in the world. The sand is olivine.

Additionally, the olivine may be released from the igneous rocks in other ways, either by simple time and erosion or, as U.S. Geological Survey (USGS) scientist Wendy Stovall explained to Mashable, "lava can erupt through ocean water in steamy, explosive events, breaking the lava into smaller pieces and fast-tracking the separation process."

A rock with olivine crystals on it
Olivine minerals can often be found on igneous rocks. underworld/Shutterstock

"It can be carried in the pumice [rapidly cooled lava] pieces that have been rained all over the area," Ganescki said. It may also be what remains when weaker rocks are destroyed by cars or foot traffic.

What some people in Hawaii are seeing is olivine rocks that "just kind of fall out" as lava is spewed into the air, according to Stovall. The process is simply sped up.

"The olivine crystals folks are finding on the ground scattered about are from violently ejected basalt [a type of lava] blobs wherein the embedded, earlier-formed olivine crystals are freed from their surrounding pahoehoe [syrupy lava] basalt liquid," Stanley Mertzman, a volcanologist at Franklin and Marshall College, told Mashable.

It's good, however, that the olivine found so far has been relatively small. Olivine is usually slightly harder than glass, so it's not something you want in large sizes raining down on your head.