Igneous rocks and minerals
Cooling history written in grain size: coarse where the melt ponded underground, glassy where it was chilled at the surface.
| Sheet | Name | Formula | Mohs | |
|---|---|---|---|---|
| ST-001 Igneous | Granite花岗岩 Granite is the rock most people name correctly and describe least accurately. It is the coarse, light-toned intrusive rock built from quartz, alkali feldspar and a little mica — but the iden Hand specimen | Quartz SiO₂ + alkali feldspar (KAlSi₃O₈) + plagioclase + mica | 6–7 aggregate (quartz-controlled) | |
| ST-002 Igneous | Granodiorite花岗闪长岩 Granodiorite looks like a slightly dirty granite and is routinely filed as one. It is the most abundant plutonic rock in the continental crust, and the difference from true granite is not co Hand specimen | Quartz SiO₂ + plagioclase (NaAlSi₃O₈–CaAl₂Si₂O₈) + hornblende + biotite | 6–7 aggregate | |
| ST-003 Igneous | Basalt玄武岩 Basalt is the most common rock on the planet's surface and one of the hardest to describe from a single specimen, because almost everything diagnostic is too small to see. It is dark, fine-g Hand specimen | Plagioclase (Ca-rich) + clinopyroxene + olivine; SiO₂ about 45–52 wt% | 5–6 aggregate (pyroxene-controlled) | |
| ST-004 Igneous | Obsidian黑曜岩 Obsidian is the geological exception that proves the rule about igneous rocks: it is an igneous rock that contains no minerals in the strict sense, because it cooled so fast that its atoms n Hand specimen | Amorphous SiO₂-rich glass, roughly 70–77 wt% SiO₂, with 1–3 wt% water | 5–5.5 (glass hardness) | |
| ST-005 Igneous | Pumice浮岩 Pumice is the only common rock that reliably floats on water, and the reason is simple arithmetic: 60 to 85 percent of its volume is gas. It is a volcanic glass foam, quenched so violently b Hand specimen | Amorphous SiO₂-rich glass with 60–85 vol% vesicles; SiO₂ about 65–75 wt% | 6 (glass, but collapses under point load) | |
| ST-006 Igneous | Gabbro辉长岩 Gabbro is what basalt becomes when it is given time. Identical in chemistry, it is the coarse-grained plutonic equivalent of the ocean floor's most common rock — and it is best known not for Hand specimen | Ca-rich plagioclase + clinopyroxene + olivine; SiO₂ about 45–52 wt% | 6–7 aggregate | |
| ST-007 Igneous | Granite vs granodiorite花岗岩与 花岗闪长岩对照 These two rocks sit next to each other in every classification chart and are routinely confused in the field, because they share their texture, their grain size, most of their minerals and t Comparison sheet | Difference is in the feldspar budget: alkali feldspar-dominant versus plagioclase-dominant | Both 6–7 aggregate; hardness does not separate them |
