Natural Connections: Minerals all around us
Is it frozen yet? Every morning for the past few weeks, I've peered into the gray dawn, looking for the absence of waves on the lake. If there wasn't a choppy surface, then I stared harder still, trying to determine if the reflection was due to calm water, or a skim of ice. One morning the pink clouds reflected on both ice and liquid, as a thin sheet filled my bay. The next morning, I couldn't see any open water.
I gave the ice another frigid day and night before venturing down to its edge. Wind had piled that first layer of ice up against the shore, and now the round pancakes of ice chunks were frozen together in a jumbled mess. Cautiously, I stepped out away from the shore, and stopped a minute to listen for cracking, and feel for shifting. Solid. I shuffled out toward the smooth ice.
Two inches of clear ice covered the deeper water. Silvery bubbles and crystalline patterns decorated the black surface. Just under the ice, little blobs of mint-green algae bobbed gently, barely moving in a gentle current. Even as the ice was freezing, these little producers had been carrying out photosynthesis and releasing oxygen bubbles, which left shimmering vertical paths in the ice as they rose toward (but never reaching) the surface.
Strange as it may seem, the surface of my lake has just become a mineral. Mineral is a geologic term, describing solid substances with certain characteristics. Minerals are all around us, but mostly overlooked. Let's take a closer look at ice to see how it fits.
The first criterion in the definition of a mineral is that it must be a natural occurring, inorganic substance. The ice on my lake is natural occurring, of course, but the ice cubes in my freezer are not. Diamonds made in laboratories are not technically minerals, either. Ice doesn't contain carbon and is not derived from living things, which means it is also inorganic.
Minerals must be crystalline solids, meaning that they have to have an orderly internal arrangement of atoms. This means that water is not a mineral, the same way that volcanic lava is not a mineral, since they are both liquids. As they cool, though, their molecules arrange themselves into distinct geometric patterns. You can see this in the hexagonal symmetry of snowflakes.
Each mineral is made of a particular mix of chemical elements, and has a definite chemical composition. The chemical composition of ice is, of course, two hydrogen atoms and one oxygen atom per molecule, written as H2O. Apatite, a mineral in your tooth enamel, is more complicated, and contains set amounts of three elements, plus variable amounts of four more.
Speaking of appetite, we are surrounded by minerals not only on a frozen lake, but also at the dinner table (especially if we relax the definition of mineral to include human-altered forms). The salt in your shaker is tiny crystals of the mineral halite (also called sodium chloride, NaCl,). The leavening in your pumpkin bread is sodium bicarbonate (NaHCO3). Both the pumpkin and the turkey contain small amounts of calcium and iron.
As you dig into the food on your plate (ceramic plate containing feldspar and silica), with your grandmother's set of heirloom flatware (silver) or your regular silverware (made of iron, nickel, molybdenum, chrome, strontium, and neodymium), be careful not to chip a tooth filling (gold)!
Give thanks for the screws (iron and zinc) that hold the feasting table together, the drywall (gypsum) that forms your cozy room, and the insulation (vermiculite) that keeps you warm. Don't forget the electric wires (copper) that power your light bulbs (tungsten, silica), and the plumbing (copper) that carries the remains of the feast away.
As you settle your stomach onto the couch with a swig of pepto (bismuth), and maybe crack a beer can (aluminum), I encourage you to give minerals a second thought. They are all around us, bringing the beauty of snowflakes, the fun of ice fishing, and the grace of good health.
"When we cut the ripe [pumpkin], should we not give it thanks? And should we not thank the knife also? We do not live in a simple world."
From "At the River Clarion," by Mary Oliver.
For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI, at 13470 County Highway M. The current exhibit, "Deer Camp: A Natural and Cultural History of White-tailed Deer," opened in May 2013 and will remain open until April 2014.