FMF - Friends of Minerals Forum, discussion and message board

[Tom Mazanec]

I was fascinated to learn that there is an official distinction between "boulder" and "cobble", etc. all the way down to clay particle.
https://en.wikipedia.org/wiki/Grain_size
This got me wondering...is there a distinction between a "rock" and a "stone"?

[Carles Millan]

It must depend on the size, I think. At dictionary.com there are several definitions. I selected those as the most meaningful:

rock: a large mass of stone forming a hill, cliff, promontory, or the like.

stone: a small piece of rock, as a pebble; something resembling a small piece of rock in size, shape, or hardness.

[Matt_Zukowski]

Neither rock nor stone are official geology terms though we use them all the time. Judging by your questions over these several months I believe that you would find it fun to read a book on mineralogy and then one on petrology (the study of rocks). You'd be well served getting a college level book on both subjects. You don't have to read or understand every word, but you can just go through the books by first reading their table of contents and then getting the gist of each chapter, and then looking though each chapter to get more info on a part of the subject.

If you'd like suggestions for particular books, just ask. Good luck.

[Pete Richards]

There is a technical geological use of the term "rock" - a rock is (in my words) a geological solid object (i.e. a common parlance rock or stone) which is made up of minerals (which are naturally occurring inorganic chemicals with specific, consistent chemical compositions, atomic structures, and properties). Rocks are named based on their mode of formation, their constituent minerals, and their grain size, mostly. A given rock may have somewhat different amounts of its constituent minerals, and so its composition is not fixed.

We all know about sedimentary, igneous, and metamorphic rocks as three main classes based on mode of formation.

Granite, gabbro, and syenite are rock terms mostly referring to rocks with different mineral components.

Granite and rhyolite, gabbro and basalt, are examples of rocks that differ primarily in grain size, the second of each pair being finer-grained.

All of this is the subject matter of petrology, the study of rocks. You can find lots of information on the web, or better yet follow Matt's suggestion and get some texts. Petrology is not the focus of this web site - mineralogy is. So while some of us know some petrology (and maybe some know a lot), this is not really the place to find out more about it!

[Bob Carnein]

FYI, MOST rocks (in the geological sense) are made up of minerals, though obsidian and pumice are glass--no crystalline material need be present. The term "stone" isn't really used in geology--it has no technical definition.

[Tom Mazanec]

[Bob Carnein]

Depending on your background, you will probably want to read the mineralogy text first, but don't become bogged down in technicalities. The most useful part is likely to be discussions about how minerals occur--their associations and why particular minerals occur in particular geologic environments.

I'd suggest a basic petrography (how to describe and classify rocks) text, rather than a petrology (more focused on genesis of specific rock types) text, if you're a beginner. Be aware that petrologists and petrographers sometimes have their own favorite classification schemes, and there are a lot of inconsistencies from one system to another. Igneous rocks are relatively straightforward, but metamorphic and sedimentary rocks are less so. Perhaps, for your needs, a good, widely accepted but rigorous physical-geology lab manual would work better than something more technical. You can buy old editions on Amazon for next to nothing, and older editions rarely are much different from later ones, at least at the beginner's level. Master the basics first, and then decide where you want to go from there.

[Vinoterapia]

Whenever I come across a book that seems interesting, I always check in Abebooks for the price of a used one. I have gotten a few bargains.