
The Rock-Forming Minerals. Geology 101: Minerals Part 3
There are roughly 7,000 known minerals on Earth. You need to know about ten of them. In the third installment of the Camp Geo Intro to Minerals series, Chris and Jesse finish the minerals chapter by working through the rock-forming minerals — the short list that makes up the overwhelming majority of the rocks in Earth's crust — and by explaining where minerals actually come from in the first place.
Before the top-ten list, they step outside the silicates. Just as the silica tetrahedron defines the silicate family, other mineral groups are defined by their own dominant anion: the carbonates (CO₃²⁻, home to calcite, arguably the second most important mineral group on the planet), the sulfates (gypsum, which Jesse grew up seeing mined in Michigan), and the phosphates (apatite — the stuff your teeth are made of, and a mineral Jesse's lab dates routinely). Along the way, Jesse clarifies a point from Part 1: an anion can be a single charged atom or a charged molecule like CO₃ or SiO₄.
Then, the four environments in which minerals grow — igneous (crystallizing from cooling magma or lava), metamorphic (solid-state recrystallization under heat and pressure), hydrothermal (precipitating from hot circulating water, as at Yellowstone and, far more commonly, at mid-ocean ridges), and sedimentary (salts left behind as cool saline water evaporates, think Bonneville Salt Flats). Chris flags the one that trips students up most: hydrothermal and sedimentary both precipitate minerals from water, but only one of them involves heat. This detour also produces the episode's best story: the day the two of them drove up a sketchy dirt road to the Gore Mountain garnet quarry in upstate New York without permission, watched a black Chrysler 300 come roaring up behind them, and left with about two tons of volleyball-sized garnets in the back of Chris's F-250.
Finally, the countdown: feldspar, quartz, the micas, the olivines, the pyroxenes, the amphiboles (hornblende, for intro purposes), the clay minerals, calcite, dolomite, and halite plus gypsum. Seven of the ten are silicates, and Chris and Jesse tie each one back to its tetrahedral structure from Part 2 — framework, sheet, single chain, double chain, single tetrahedron. They cover the tricks for telling calcite from dolomite (a drop of HCl fizzes like Alka-Seltzer on one and like flat pop on the other), why mica rarely survives in sedimentary rocks, why clay minerals are basically what feldspar turns into when it hits a stream, and Chris's field-tested (and decidedly not medically endorsed) use of crushed limestone as heartburn relief.
The episode closes with Jesse's quiz question for Chris, which Chris promptly declares "has potential" but needs reworking.
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