What is in a name? Identifying rocks, which is somewhere our curiosity should naturally lead us, can be a tricky business.
I have a large and growing ring of rocks in my yard that I hope to make into an interesting display someday. Right now, the ring is not in any recognizable order. The rocks are not grouped by the three categories by which they were formed, igneous, sedimentary, or metamorphic. They are not grouped by any type, quartz, limestone, granite, or chert. They are not organized by size or shape or the minerals that give them color, iron red, copper green, or manganese black. Mostly they are in the order in which they were collected. The earliest finds are in the center, the most recent along the edges. To walk along this flattened heap is to go back in time and revisit those places where they were picked up.
I want to learn the names of rocks as a step to understanding the geology that created them. I wonder about the layers that I see on every drive through a highway road cut, like the ones you pass through on Highway 82, southwest of Patagonia, around mile marker 12. There is an interesting story there, a narrative hiding in plain sight if only I could decipher the language that it is written in.
I get that same sense of wonder when I drive along Highway 90, on the east side of the Whetstones, on the way up to Benson. There you can see dipping sedimentary strata, which were originally horizontal but were later tilted due to tectonic uplift. An orogeny is a period of mountain-building, and during the Laramide Orogeny, 80 to 40 million years ago, the Farallon Plate was being subducted beneath the North American Plate at a place about where California is today. Because at the end of the subduction the Farallon Plate lost its steep pitch, the force was more lateral causing the buckling and uplift to occur where the Whetstones are located today.
When I first started collecting, I was excited to discover a Rock Identifier app that I could carry around on my phone. Wow, I thought, how easy is this? Take a picture, upload, and wait a few seconds, and voila, instant knowledge.
My wife has a plant identifier app, and plants can be quickly narrowed down based on a silhouette of their leaves. The leaves and stalks may be nearly infinite in their size variation but are rather finite in their shape variation. This makes it easy for an algorithm to crawl the pixels in a photo and arrive at a conclusive identification.
Rocks, on the other hand, seem to have infinite variations along multiple axes. Size, shape, texture, hardness, color, gross structure and fine structure, to name a few. There seems to be general agreement in the rockhound communities that exist online that the apps, based on photos to identify, are just not that reliable.
So, how to identify rocks? While a gas spectrometer or a scanning electron microscope can give definitive answers, they are not the most practical items to keep in your garage. Geologists and weekend warriors alike can narrow down the answer to the question, “What the heck is that thing?” by carrying a simple kit of tools to make a field identification.
One of the first things to determine is the specimen’s hardness on the 1-10 Mohs Scale. A copper penny, (get ’em while you can), a pocketknife, and a piece of glass can tell you if your score is a 3, around a 5, or above 5. A small magnet is enough to inform you of your rock’s possible iron content. An ultraviolet light can detect fluorescence which would be indicative of calcite, fluorite or willemite. A magnifying glass or a jewelers’ lens can help with fine crystal structure. An acid bottle and an eye dropper, containing a weak hydrochloric acid solution or simple vinegar can tell you immediately if that whitish crystal structure is calcite or quartz because calcite will fizz on contact.
Last, but not least, is an unglazed porcelain tile so that you can perform a streak test. Does it leave a streak? If so, what color?
I have recently ditched my Rock Identifier in favor of my Chatbot. The old app would produce three probabilities, sometimes wildly divergent. Gee, my digital assistant, when shown a photograph, offers possibilities too, but then asks questions in return to walk me through the field identification process.
Would a rose, by any other name, still smell as sweet? A tricky question, and definitely not an original line.
Keith Krizan can be contacted at therealkbkkbk@gmail.com.