In late September I was in Swede’s, the famous light blue jewelry and rock store in the middle of Copper Harbor, Michigan. The feisty woman in charge, 83-year-old Mary Billings, asked me as I walked in–“What is the gemstone of Michigan?”
When I answered, “Isle Royale Greenstone,” she looked at me with new respect.
“You’re only the thirteenth customer this season who has answered that question correctly. And we’ve had a lot of people who’ve walked through that door.” She shook her head, a little disgusted that Michiganders weren’t commonly aware of their state gemstone.
Most people, if they have any idea at all, would probably say Petoskey is the state’s gem. And it IS the state rock. But Isle Royale Greenstone, or just Greenstone, has been Michigan’s official gem since 1973. Found mainly on Isle Royale or the Keweenaw Peninsula, Greenstone has the fancy, scientific name of Chlorastrolite, which is a variety of the mineral Pumpellyite. It’s often found in and around copper mines, which are abundant in the Keweenaw. The mineral makes its home in amygdaloidal basalt. If you’re like me, that phrase holds no meaning. I had to look it up, so I’m happy to share its meaning. Basically it’s a pit or cavity in the stone. So amygdaloidal basalt is cooled and hardened lava with lots of cavities in it that have been filled in with minerals.
Once the Greenstone is removed from its host rock, it can be cut and polished. But it’s a tricky stone to work with because it’s not really hard–only a 5-6 on the Mohs’ Scale– and it can have its own cavities and hollow spots within it. Cutters want to expose the best “turtle-back” pattern that they can and eliminate any bad spots. But removing a top layer of the stone is likely to reveal a different, and not necessarily better pattern. The goal is a clear pattern showing some chatoyancy. The best stones will demonstrate that change in luster as they are tilted back and forth in the light.
Greenstone is not a particularly expensive gemstone to buy. Even with the labor involved in finding, mining, and cutting it, there’s just not a huge market for the material. But it isn’t an easy gem to own. Since the year 2000, it’s been illegal to take Isle Royale Greenstone off the island. The island is, after all, a national park. And even Keweenaw Greenstone isn’t easy to get unless you have access to the copper mine areas. Most jewelry stores, even in Michigan, don’t carry Greenstone. So plan on spending some time searching for your perfect piece of Michigan’s gemstone. Whether you spend time looking along the shoreline for a rare small piece of it, or whether you search for jewelry stores that carry the gem, enjoy the journey.