Minerals

 I hesitate to post this: it can be intimidating. But it does give a breakdown on how

the vocabulary of Geology settles 😂

Geology; rocks can be classified sructurally or by chemical composition. Are there distinct categories for these two classes?

Absolutely — geologists really do use two parallel classification systems, and each has its own distinct categories. Think of them as two different “lenses” for understanding the same rock.

Below is a clean, structured breakdown.

🪨 1. Structural (or Textural) Classification

This system focuses on how the rock is put together — its fabric, grain size, layering, and formation process. It does not care about the exact minerals at first, only the physical structure.

Igneous Rocks — Structural Categories

Plutonic / Intrusive (coarse‑grained, slow cooling)

Volcanic / Extrusive (fine‑grained, fast cooling)

Glassy (obsidian)

Porphyritic (mixed grain sizes)

Vesicular (full of gas bubbles)

Pyroclastic (fragmental volcanic debris)

Sedimentary Rocks — Structural Categories

Clastic (made of fragments: sandstone, shale)

Chemical (precipitated: rock salt, travertine)

Biogenic / Organic (shells, plant material: limestone, coal)

Grain size classes (conglomerate, breccia, siltstone, etc.)

Bedding structures (laminated, cross‑bedded, graded)

Metamorphic Rocks — Structural Categories

Foliated (layered due to pressure: slate → schist → gneiss)

Non‑foliated (no layering: marble, quartzite)

Lineated (mineral alignment)

Granoblastic (equigranular textures)

Structural classification = “What does it look like and how did it form?”

🧪 2. Chemical (or Mineralogical) Classification

This system focuses on what the rock is made of — the minerals and chemical composition.

Igneous Rocks — Chemical Categories

Felsic (high silica: granite, rhyolite)

Intermediate (andesite, diorite)

Mafic (basalt, gabbro)

Ultramafic (peridotite, komatiite)

These categories reflect silica content, iron/magnesium content, and mineral assemblages.

Sedimentary Rocks — Chemical Categories

Carbonates (limestone, dolostone)

Evaporites (halite, gypsum)

Siliceous (chert)

Iron‑rich (banded iron formations)

Phosphates (apatite-rich rocks)

Metamorphic Rocks — Chemical Categories

Metamorphic rocks are often grouped by protolith chemistry:

Pelitic (clay-rich protoliths → schist, gneiss)

Mafic (basaltic protoliths → amphibolite)

Carbonate (limestone → marble)

Ultramafic (peridotite → serpentinite)

Quartzofeldspathic (granite → gneiss)

Chemical classification = “What minerals and elements are present?”

                                                                 

                                                 'mafic' is dark, and 'pelitic' is light-colored                

If you want, I can help you classify a rock you have

You can describe:

grain size

color

layering or foliation

hardness

reaction to acid

magnetism

context (riverbed, volcanic area, quarry)

And we can walk through both classification systems together.

Where would you like to take this next — structural vs chemical in more depth, or applying the categories to real samples?

Mineral Properties, Photos, Uses and Descriptions

                                                                         *     *     *

https://geology.com/minerals/graphite.shtml

Graphite is the stuff  of lead pencils we all own, long appreciated as a soft form

of carbon. But is also currently plays a role in the production of electrical vehicles. 

It is not in-itself a rare mineral, but it is an extension of the category. 

                                                                                   

source: Wikipedia

source: Anton Leskov

https://natural-resources.canada.ca/minerals-mining/mining-data-statistics-analysis/minerals-metals-facts/graphite-facts