I’m much more knowledgeable writing about the living components of the ocean ecosystem than the non-living parts, but when my cousin came up for a visit last summer and showed me garnets in the rocks along the shore, my interest was sparked. He’s a retired geologist with a great depth of knowledge about rocks and an ability to explain it in a way that made it seem magical. Perhaps it is the way that he whimsically answered the questions my girls asked about the origin of rocks and minerals that involved industrious trolls working underground to create sparkly gems that turned my usual boredom with rocks to fascination.
Perhaps it also had something to do with the fact that garnet is also my girls’ birthstone and here it was right on our shore peeking out in tiny bright speckles along the seam of an otherwise non-descript round white rock. I had no idea there were gems in Maine’s rock aside from the ubiquitous quartz. Apparently, this is just one of many gems that are in Maine rocks.
So, where do these gems come from and how are they made (if not by the rock trolls)? This was one of the many questions my girls posited as a part of what became our “Rocks with Rick” sessions during homeschooling this spring. Gems are a type of mineral – the clearest and most crystalline of the bunch. And, minerals are the basic materials that make up rocks. Common minerals are feldspar, quartz, olivine, mica, calcite, and magnetite. Feldspar is a big group of minerals. Riverside mills used to process feldspar for industrial uses like in ceramics and enamels. Quartz is the clear, white-ish crystal material you see in streaks along seaside granite, olivine has a color to match its name, mica is the silvery shiny flecks that flake off of rocks, and magnetite is a very dark magnetic mineral. Calcite is white and is a relative of calcium – one of the minerals you might see listed on the nutrition panel of your cereal box. These minerals get into our food through the plants that make up our food. These plants take them up from the soil (which is just broken down rocks). So, while you don’t eat garnets in your food, you do consume many of the same minerals in your food that are found in the rocks along the seashore.
What these rocks look like is not just determined by what they are made of, but also what happens to them both inside the earth and once they come to the surface. Most of the rocks come from the molten center deep inside the earth including those like the black basalts that come out in volcanoes. However, the granite we have in Maine comes from just below the surface. More changes happen to the rocks once they emerge from the earth. That’s when they become sedimentary – like sandstone that is the remnants of old ocean floors that have been compacted over time. These also often contain fossils. They other type is metamorphic – these metamorphose from one form to another just like a tadpole to a frog. This can happen from pressure or heat or some combination. If you look at the granites along the shore, you can often see wavy patterns where the rock has melted, been squished down and reshaped before hardening again into fantastical patterns.
There is so much to see in the rocks and stories that they tell of where they came from (perhaps including a few trolls). Finding garnets in the rocks was the impetus to look harder and much more closely. It turns out that one of the non-living components of the seashore that I often overlooked has much more life and history to it than expected. Thanks to my cousin for sparking a new curiosity in a subject that is easy for anyone to explore and can help you to understand the complexities of our coastline more fully.
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