Monday, July 18, 2011

Index Mineral - GEO 056


GEO 056
Kyanite 
Class: Mineral
Location: Brazil

It's another scorching hot day here so just a quick post to hold you over. This is a nice larger mineral specimen heralding all the way South from Brazil. Kyanite is its name and it gets its name from the Greek word meaning 'blue' (for obvious reasons). Though don't take it that all Kyanite is blue, like many other minerals it can have a variety of color shades. This one also comes in white, gray, green, and black, though blue is the most commonly found type. Remember that to identify minerals you can't just use the physical properties (i.e. color/shape/taste in some cases but don't go around licking rocks), you must also use the properties such as hardness, streak (the color produced when rubbed on a streak plate, it's not always the same), density, crystal lattice, and of course chemical composition. Kyanite is made up of Aluminum (Al), Silicon (Si), and Oxygen (O) with a chemical formula of Al2SiO5. It has fairly good cleavage (roughly meaning it forms sheets), has a hardness of between 4 and 7 on Moh's Scale of Hardness, a white streak, and has a fibrous habit for growing. 

What's interesting about Kyanite is that it's an index mineral. Much akin to how index fossils are used for relative dating of the surrounding fossils, this mineral is used for finding the approximate temperature/pressure of the surrounding rock. This is because Kyanite is normally found in metamorphic rocks and is normally found above 4kB of pressure. If you take a look at this metamorphic mineral phase diagram, you can see that the triangular shaped chunk in the upper left-hand corner is Kyanite and if you know what the temperature is and you find a certain mineral you can estimate the pressure, or if you know the pressure and a mineral you can estimate the temperature at which it formed, though this is just a rough sketch of how to use it. It's other main uses include being used in dishware and electronics. And as always you can find more information concerning this interesting mineral Kyanite here. 

No comments:

Post a Comment