Pikes Peak Pebble Pups

Pikes Peak Pebble Pups

Thursday, May 18, 2017

The Mysterious Blue Orbs of K2 Granite

William Wray

K2 granite, with impressive splashes of blue circles or orbs on its surface, is a rock from a rarely visited site in the Himalayas.  The blue circles are azurite inside of white K2 granite rock. The white granite is fine-grained and composed of these minerals: quartz, feldspar, muscovite, and biotite. The azurite stained parts of the granite, making blue dots, which range from a couple of millimeters to about two centimeters.  Azurite has a relative hardness of 3.5-4 on the Mohs hardness scale, but assumes the hardness of the white granite because the azurite is only a stain.  The azurite formed after all the other minerals in the granite had cooled and hardened.  With a hand lens or microscope, azurite spheres reveal that the azurite appears along the edges of mineral grains, in tiny fractures in the granite, and in feldspar grains. 

Since azurite and white granite are rarely found together, people don’t think the blue orbs are azurite, and commonly think of it as simply a blue dye added to make the rock a novelty.  Scientific tests have not been made, so the jury is still out on the blue orbs in this interesting rock.  There is lively debate on mineral forums, including Mindat.org, about the nature of the blue orbs. 

An oval cabochon made from K2 Granite  found on K2, a mountain between Pakistan and China, revealing several bright blue azurite stains. The blue azurite stains formed after the granite cooled and hardened.  Photo © by the author. Specimen from the William Wray collection.

K2 granite is found near the base of K2, the mountain it is named after, in the Himalayas. K2, also called “Mount Goodwin Austen” is the second highest mountain in the world, rising up at 8,611 meters (28,253 feet).  K2 got its name from the British surveyor T.G. Montgomerie.  The “K” comes from the Karakoram mountain range and the “2” means that it is the second tallest peak recorded. 

A view of K2, summer 2006.  At 8,611 meters (28,253 ft) this mountain is ranked second largest in the world. Note the large valley glacier flowing out of the mountain.  Photo by Svy123. This image is licensed under the Creative Commons Attribution 3.0  license.

K2 granite is an excellent lapidary material. It cuts and tumbles well because of its high feldspar amount, and it can be easily shaped on a diamond wheel.  K2 is durable in jewelry because the feldspar has a hardness of 6.  K2 granite will scratch over time and is not suitable for bracelets or rings.  K2 granite is not very pricey, and excellent specimens can be bought for about $30 to $40 at gem shows and other venues.  K2 granite is a colorful specimen, and its bright blue azurite orbs will make it a nice addition to your collection of curiosities.

Meet the author:   William Wray is a fifth grader at Lake George Community Charter School.  He is a prolific reader with a love of all things nature related—from rocks and fossils to animals and plants. He attends the Pikes Peak Pebble Pups in Lake George, Colorado and participates there as an Earth Science Scholar. 

For Further Reading

K2 Granite: A white granite with azurite - AKA K2 Jasper. (n.d.). Retrieved from http://geology.com/gemstones/k2/

Nicholas Varnay and K2 — The Practical Gemologist. (n.d.). Retrieved from http://www.thepracticalgemologist.com/gemstones-2/2015/5/22/pick-of-the-week-nicholas-varnay-and-k2

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