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In metallurgy, an ore is defined as that mineral from which metal can be obtained with economic viability.
I have also read that ores are rocks from which minerals or metals can be extracted profitably.
If ores are rocks they cannot be minerals as rocks are aggregates of mineral and vice versa, so which of these is actually correct?

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  • $\begingroup$ Correct is whatever definition you hold to be correct. "Rock" is of course a stupid category here, because usability as "ore" is given by chemical composition and perhaps microstructure, but not particle size. $\endgroup$ – Karl Nov 26 '16 at 12:38
  • $\begingroup$ @Karl , usability of an ore is given by chemical composition, do you mean to say that usability of an ore is from the mineral since minerals have a definite chemical composition with a crystalline structure? So that would imply that ores be defined in terms of minerals but an ore contains other minerals in addition to the mineral from which metal would be extracted, then by definition it is an aggregate of minerals which makes it a rock $\endgroup$ – Kaberi Ghosh Nov 26 '16 at 12:45
  • $\begingroup$ Minerals (per usual definition) are unadulterated solids as appearing in nature, while ore is raw material for a plast furnace or similar process. Two completely different categories. $\endgroup$ – Karl Nov 26 '16 at 13:01
  • $\begingroup$ Could you explain that point? Isnt it that all ores are minerals but not all minerals are ores, is that right? $\endgroup$ – Kaberi Ghosh Nov 26 '16 at 13:07
  • $\begingroup$ Processing the ore mineral to the stuff that is finally fed into the blast furnace can involve a number of processing steps. All the way however, it is called "ore". $\endgroup$ – Karl Nov 26 '16 at 13:35
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Some of the terms are pretty vague and it isn't worth getting hung up on a precise definition.

Of the terms you use, "rock" is the vaguest. I means just about any hard thing you find in nature (and even that last qualification isn't precise as some people might call something like concrete an artificial rock). You can't infer anything much from the term "rock". Sometimes geologists might classify particular rocks into useful categories such as sandstone, granite or limestone. But the term is vague enough that rock formations might have more than one type of rock in them.

Ore is a more specific term. It does have a meaning but that meaning can change over time. Generally an ore refers to whether a useful product can be economically extracted from something. So if a rock formation contains a small amount of gold then it would count as an ore if the cost of extracting it was less than the amount the resulting gold could be sold for. But, sometimes, a geologist might refer to a particular mineral as the ore from which the desired substance is extracted. For example, she might call galena an ore from which lead is extracted. But this ignores the fact that galena is found in formations that contain many other minerals and has to be separated from them to be useful. More precise usage would be to define the ore as the rock formation containing enough galena for economic extraction of lead.

A mineral is usually a very precise term referring to a pure substance. Rocks are usually made of mixtures of minerals. Granite, for example, is made from quartz, feldspar and mica. The separate crystals are usually large enough to see with the naked eye.

An ore is simply a rock formation (which might contain more than one type of rock) where one of the minerals in it is economically valuable.

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Which definition of an ore is correct?

None. A "definition" is an artificial idea made up by people to describe something. And even then, people have to actually use that definition correctly so it will have any value. Also, the usage of a certain definition differs between fields (geologists, economists, engineers, etc)

I am an ore deposit geologist, so I am familiar with the subject. Usually people describe a rock as a collection of one or more minerals together, where a mineral is a naturally occurring substance with a crystalline structure. Note that this definition does not include obsidian because it's glassy or any amorphous materials because they're not crystalline (where they are obviously rocks!).

Ore is usually considered (by geologists) as a rock with some kind of economic commodity that you can extract at a profit. Engineers will consider ore to be the thing you mine and put into the smelter, and minerals as the stuff that geologists consider ore. These are all applied very loosely. Ore doesn't even have to be extracted at a profit (because this changes with time, technology, and prices). As ore geologists, we name everything that has something even remotely interesting economically as an "ore deposit".

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