That’s a good question. On Isle Royale, greenstone has two entirely different meanings.
Hiking along Isle Royale’s loftiest ridge, you might encounter an outcropping of basalt with a greenish hue. Welcome to Greenstone Ridge, backbone of Isle Royale and its highest and longest ridge. Running more than 40 miles along the ridge, the Greenstone Trail provides excellent island-wide views. The ridge is named for the color of the underlying Greenstone Flow. This basalt flow is up to 800 feet thick and extends deep under Lake Superior in a continuous flow which reappears 50 miles later, on the Keweenaw Peninsula in Michigan. It is one of the earth’s largest and thickest lava flows.
Strolling along a pebble beach on Isle Royale, you might stoop down and find a pea-sized greenish pebble amongst myriad other stones. Upon closer examination, you may be looking at the mineral pumpellyite, the "Isle Royale Greenstone" and Michigan’s state gemstone. Chlorastrolite, which means "green star stone," is uncommon outside of Isle Royale. Chlorastrolite originates in lava flow cavities, is weathered out, and then is washed out into Lake Superior and sometimes wave-washed onto beaches. These stones usually show a mosaic or segmented pattern of "facets," sometimes called "turtleback." The facets are symbolic of the many faces Isle Royale’s wilderness shows. As with the greenstone, each facet is unique and integral to the whole. And just as untrammeled land across the face of the United States was once much more common, so were greenstones and related minerals on Isle Royale beaches and under Lake Superior.
In 1997, in a remote campground, Rangers found ten large zip lock bags filled with over 300 pieces of datolite (a semi-precious gemstone) that two individuals had collected from Isle Royale’s Lake Superior waters. A reexamination by the U. S. Attorney’s office and Interior Department lawyers of mineral collection laws revealed that the submerged Lake Superior minerals are afforded the same protection under Park Service-wide regulations that protect all natural, cultural, archeological, and mineral resources. What this means is that the traditional use of beach combing, looking for greenstones, agates, and other mineral can continue, but visitors can no longer collect and keep them. Instead, visitors can enjoy their discoveries via photographs, drawings, and memories. Many old time collectors admit that the quantity and quality of minerals had become scarcer due to years of collection. This new protection ensures that these nonrenewable resources will continue to be seen and may even increase through storm deposition, allowing for generations yet unborn to enjoy them.
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