Raining Peridot From Hawaiian Volcanos
Taking a sample of fresh lava using a rock hammer on the Kalapana Coast in 2013. (Christine Lopez, 2013)
Kilauea’s Main Crater— Halema’uma’u (Christine Lopez, 2013)
There’s this claim we keep seeing pop up around the internet about the Kilauea volcano in Hawaii and I thought I would talk about it because I studied similar volcanic processes in my igneous petrology class at UCLA. We were lucky enough to take a week long field trip to the big island of Hawaii to study volcanology and had the amazing opportunity to see the science behind the claims being made first hand. As a GIA Graduate Gemologist with a background in geology, I couldn't resist writing about it.
The story goes like this: Gem quality peridot specimens of cuttable size erupted from the ground in the Puna District of the Big Island with so much force that day that they flew up into the air and rained back down to the ground where they were collected by bewildered locals. Woah.
So is Hawaiian Peridot real and did it actually rain gemstones during the 2018 volcanic eruption on the Big Island? This story has become the stuff of urban legend so let’s talk about it.
What sets a gemstone apart from a mineral specimen?
First things first, let’s talk about gemstones and what makes them so special. A gemstone is typically composed of a coveted rock, mineral, crystal, or organic material that is cut or polished in a way to enhance its beauty, clarity, or desirability. Gemstones also have value and a market that demands them for their collectability and use in either jewelry, fashion, or objects of art.
A photo taken from inside a very old lava tube overtaken by the jungle looking up at a skylight caused by the ground above the tube collapsing in on itself. Although the lava is cooled into basalt rock, lava tubes remain a dangerous and deadly feature of volcanic environments because they can collapse without notice. (Christine Lopez, 2013)
Peridot is the name for gem quality and sized specimens of the mineral Olivine. This semi precious gemstone is always green, was historically used in ancient jewelry, and the birthstone of August. Peridot was a favorite of Cleopatra during the age of antiquity and is still very popular with modern jewelry designers today.
So what makes a specimen of the mineral olivine qualify to be called the gemstone peridot?
Weight: Must be of large enough size to hold value on the market.
Clarity: Must be free of eye visable inclusions, cracks, and defects that take away from the durability and potential beauty of the stone.
Shape: Must be of a usable shape meaning it must be large enough in all directions to cut a gemstone from.
Not all gemstones are minerals and not all minerals are gemstones.
The Science Behind Hawaiian “Peridot”
Kilauea is one of several volcanos that make up the Big Island of Hawaii and has been vigorously erupting since 1823 and rightfully has the title of being the world’s most active volcano. The now infamous 2018 eruption that introduced the idea of gemstones raining from the sky began on May 4th in the lower Puna District as the world watched the cataclysmic destruction of homes and the violent birth of new land.
A look inside a newer but currently inactive lava tube. Notice how the curved linear structures follow what would have been a a subterranean river of molten rock. The red and orange colors on the rock are signs of oxidation, one of the early steps of decomposition experienced by these types of volcanic rock.(Christine Lopez, 2013)
Although common in Hawaiian volcanic rock, most olivine found on the Big Island cooled too quickly to form eye visible gem quality peridot. Due to quick cooling, the chemistry of the volcano, and the fact that Kilauea is hot even for a volcano, it is rare to find the crystallization of eye-visible crystals, let alone anything useable in jewelry. This is why we do not see commercial or artisanal mining operations for peridot in Hawaii. Eye visible crystals of olivine are typically only found on the inner walls of volcanic vents and craters in Hawaii. This olivine is trapped in the rock it was formed in and must go through weathering by the means of wind, rain, and time to release these tiny sand sized crystals from their host rock.
It is believed that the small olivine crystals ejected in the Puna District in 2018 were likely transported from the main Kilauea crater— Halema’uma’u. When the big lava lake drained, it transported the olivine-bearing rock to the Lower East Rift Zone in the Puna District below the summit by the means of lava tubes. Lava tubes work a lot like the plumbing in your home, they are essentially a system of connected drainage channels with a flow influenced by gravity and path of least resistance. During transportation by lava, the rock carrying the small olivine crystals that once lined the main caldera would have been mixed in with the fresh lava but this did not greatly affect the olivine as this mineral is extremely resilient in volcanic environments. After all, if Olivine can survive the earth’s firy mantle, a little lava is really no big deal. The olivine recovered from this event is in the form of tiny barely eye visible crystals still stuck in its partially remelted volcanic wall host rock, far from the loose cuttable gemstones claimed in the story.
The Verdict
Although the claim that Kilauea was erupting gemstones that fell back to earth like rain was not completely true, what actually happened is still geologically fascinating. Many of the photos shared on social media or by the media then and now show sizable peridot crystals from other sources around the world like Arizona and Pakistan. Take a look at the specimen below to get a better idea of what was really erupting from Kilauea back in 2018.
Although Hawaiian olivine crystals are not exactly gemstone quality peridot and rarely eye visible, we can all appreciate the power and beauty of the volcanic island that created them.
This is a photo of an unrelated specimen containing very small olivine crystals that was found in 2013 near Kalapana on the big island of Hawaii. This specimen would have been transported in a similar way to the olivine we are discussing and is far from what a gemologist would consider gem quality material. (Christine Lopez, 2013)