By Popular DemandA friend suggested that I could increase my readership if the blog featured more cleavage. So, as an experiment, I have decided to give it a go.
What Is Cleavage?
The orderly arrangement of atoms in a mineral can be seen in its tendency to break along smooth planes in specific directions --- a property known as cleavage. The planes are known as cleavage planes. A mineral's ability to resist breakage depends on the strength of chemical bonds between the atoms in its crystal structure. The stronger the bonds, the more difficult it is the break the mineral.
What makes a chemical bond "strong" or "weak?" In simple terms, the strength of a bond depends on the intensity and the shape of the electrical field (the complex cloud of electrons) between two atoms. Describing the electrical field and all of the factors that control its intensity and shape, however, is a very challenging task. To do it, chemists measure physical and electrical properties of each atom and use those measurements to describe the bond mathematically. One of the most important measurements is the distance between atoms. As a rule of thumb, the closer two atoms are to each other, the more tightly they bond together, all other factors being equal.
In most crystal structures, atoms are closer together in some directions than in others. Thus, the bonds in those directions are stronger. Cleavage takes place along planes that cut across the longest, weakest bonds in the structure.
Some minerals, such as the micas, cleave in only one direction. Others, in which more than one set of layers is weakly bonded, may cleave in two or more directions. Geologists can use the number of cleavage directions and the angles between them to distinguish one mineral from another. For example, the four cleavage directions in the mineral fluorite, pictured above, produce perfect octahedral fragments --- a very distinctive characteristic of that mineral.
Some minerals, such as quartz, do not exhibit cleavage at all, because there is little difference in bond strength from one direction to another in their crystal structures. Such minerals break to produce a rough, non-planar surface called a fracture instead.
Your Input
If you have found this information useful, let me know. Right now, I'm researching hose. My friend also said if the blog featured more hose, I would see a corresponding uptick in readership. This is hard work!
4 comments:
Now that's some cold volcano logic!
Have you seen the volcano death grip?
My mother would like this information. :)
As for the other kind of cleavage: sheesh, first blue-footed boobies and now this?? :Þ Actually, someone once remarked that my previous livejournal reminded them of "a Disney movie ... with brains and cleavage." *L*
I'm so ashamed.
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