MTPR

Malachite: Brilliantly Green, And Made In Montana

Nov 5, 2015

   

Never having seen such a brilliant green like this in nature, I was certain it was melted plastic or some other man-made material. Paint. It had to be paint. I tried to scrape the enamel off of the dolomite matrix, but to no avail. As I looked about, I saw that scant splashes of this enigma were all around me.

Skirting along the side of Mount Jumbo, I was trying to keep my footing along a talus pile. The limestone cobbles wobbled underneath my boots. It was taking a very concerted effort on my part to keep my eyes ahead, as I had lost the trail, and I was watching where I stepped. The ground flattened out and I was finally able to scan the foreground for treasures.

A large piece of quartz on the hillside caught my eye. I scrambled up to get a closer look, and upon closer inspection, I realized it wasn’t quartz, but dolomite. I picked around the scree for any large crystals. In my periphery, a blaze of viridian gleamed as the rocks turned over, piquing my curiosity.

Never having seen such a brilliant green like this in nature, I was certain it was melted plastic or some other man-made material. Paint. It had to be paint. I tried to scrape the enamel off of the dolomite matrix, but to no avail. As I looked about, I saw that scant splashes of this enigma were all around me.

I didn’t have my rock hammer with me, so I lifted up the rock and heaved it onto another, breaking it open. The dolomite cleaved, chunked apart, and exposed oxidized scabs of the mystery mineral. I chose the best-looking specimen, put it in my pack, and headed down the hill. I took a picture of my hand sample and fired it off to my former geology professor.

What is this? He replied back quickly, informing me it was malachite. I was in copper country.

Malachite, a copper carbonate mineral, forms when chemical weathering breaks down copper ores that precipitate into the cracks and crevices of the surrounding rock, usually limestone (the source of the carbonate). These crevices fill up with the mineralized fluid and the water evaporates, leaving acid green rivulets behind. Indeed, upon inspection of my own sample, it looks as though the rock will disintegrate under the caustic brightness.

Because of its striking color, malachite is mined for its lapidary uses, producing remarkable gem and sculpture materials, and used for everything from jewelry and small decorative pieces to items such as the “Tazza,” a large vase that was a gift from Tsar Nicholas II and is one of the largest pieces of malachite in North America. I tried to envision a piece of the mineral large enough to construct a several-foot-high vase. I doubted my scant amount would yield anything larger than a quarter.

Specimens such as my hand sample are non-crystalline, meaning they do not form crystals, and have an earthy luster to them. I knew that my malachite wouldn’t be polished down for jewelry, but it is serving an ornamental purpose. It sits on my kitchen windowsill, where I can marvel at the chromatic wonder the earth creates. 

 

"Field Notes" is produced by the Montana Natural History Center.

(Broadcast: "Fieldnotes," 10/18/15 & 10/23/15. Listen on air or online Sundays at 12:55 p.m., Tuesdays at 4:54 p.m., and Fridays at 4:54 p.m., or via podcast.)