Engineering geology

What Is a Rock?

In contrast to minerals, rocks are more loosely defined. Simply, a rock is any solid mass of mineral, or mineral-like, a matter that occurs naturally as part of our planet.
The term aggregate implies that the minerals are joined in such a way that their individual properties are retained. Note that the different minerals that makeup granite can be easily identified. However, some rocks are composed almost entirely of one mineral. A common example is the sedimentary rock limestone, which is an impure mass of the mineral calcite.
In addition, some rocks are composed of nonmineral matter.
These include the volcanic rocks obsidian and pumice, which are noncrystalline glassy substances, and coal, which consists of solid organic debris.
Although this chapter deals primarily with the nature of minerals, keep in mind that most rocks are simply aggregates of minerals. Because the properties of rocks are determined largely by the chemical composition and crystalline structure of the minerals contained within them, we will first consider these Earth materials.

23 thoughts on “What Is a Rock?

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  3. I really enjoy this site therefore as a student of geology I am proud to be part of this site thank you.

  4. What is the main difference we see in granite rock familes like granodiorite, pegimatite, Quartz-biotite??

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