WHAT IS A MINERAL?
WHAT IS A ROCK?

"What'ya got, Lou?"
"Beats me! But I think I could grow fond of it!! What do you think it is, Lulu?"
"Well let me ask you: Do you think someone made it?"
"Nah! I broke it off a cliff!"
"OK, so it's natural! Next, do you think it is or was alive?"
"I hope not! What are you getting at, Lulu?"
"Answer this: Is it a solid, liquid or gas?"
"You are persistent! It's a solid!"
"OK! One more question! Do you think it's the same throughout?"
"That's not an easy question! It looks pretty uniform, except when I look at it from a certain direction I see colors! What do you mean by 'same'?!"
"You're right Lou, I'm not being clear! I mean, do you think it has the same composition throughout? Do you think if you broke it into a hundred pieces, each would have the same proportions of chemical elements? Be made of exactly the same stuff?"
"How should I know?"
"How should you know indeed!! We need to take an X-ray picture of it to see if the atoms out of which it is made are arranged randomly - in which case no two pieces are likely to have exactly the same composition - or if the atoms are arranged in an orderly fashion - in which case every piece would have pretty much the same composition!"
"Sounds good to me!!"
"So, which one is it??!"
"This one!"
"That means it's a mineral!"
"What's a mineral!?"
"A mineral is any natural, inorganic (not living) solid, whose atoms are arranged in an orderly fashion! And as a result of the orderly arrangement of the atoms, the object is uniform throughout. The proportions of the different atoms are fixed. From the X-ray of this mineral we can see that the ratio of red to white atoms is one to one throughout the specimen! If the atoms were arranged randomly, the ratio of red to white atoms would vary from one part of the specimen to another!"
"Are there any natural, inorganic solids whose atoms are arranged randomly!?"
"Yes! A common example is natural volcanic glass!"
"So what makes one mineral different from another?"
"You're asking such good questions, Lou! What makes a particular mineral what it is, is this: (1) its chemical composition (which atoms it's made of) and (2) how the atoms are arranged!!"
"Even though their atoms are arranged the same way, Mineral A and Mineral B are different minerals because they have different chemical compositions!!"
"I get it! And even though Mineral B and Mineral C have the same chemical composition, they are different minerals because their atoms are arranged differently!"
"Good thinking, Lou! But let's carry that one step further! There are some minerals that have their atoms arranged in the same way, and whose compositions are almost, but not quite identical! Such clearly related minerals are said to belong to the same 'mineral family'. Click on ye old button to visit the Mineral Family Homestead!
"Been there! Done that! Quite a place!"
"You're a good man, Lou! Now you're on your way to becoming a Mineralogist!!"
"But now I've got another question! I understand what a mineral is, but what's a ROCK?!"
"Look at these pictures of rocks and then you tell me, Lou!!!"
"They all seem to be made of things stuck together!"
"You got it! Rocks are mixtures of minerals and other things that have become attached to each other!! The other things can be objects such as shells, bones, volcanic glass, or smaller rocks!"
"Wow! Is the whole greater than the sum of its parts? I feel in danger of becoming a geologist!!"
"Either that, Lou or a philosopher!!!"

2010, David Leveson/Revised by G.Rocha and Michelle O'Dea