2. How do the crystal structures of pyroxenes and amphiboles differ from one another?

Pyroxenes are single chain silicates, with each silica tetrahedron sharing two oxygens with neighboring tetrahedra.  Amphiboles are double chain silicates, with each silica tetrahdron sharing two or three oxygens with neighboring tetrahedra.

5. What is the distinction between cleavage and external crystal form?

Cleavage is the ability of a mineral to break along prefered planar directions.  When a mineral breaks, it breaks along certain cleavage planes.  Crystal form is the shape that a mineral takes when it is allowed to grow freely into an open space.  An example is the hexagonal prism shape found in quartz crystals.

9.  What are the three most common elements (by number and approximate percentage) in Earth's crust?

O, 46.6%; Si, 27.7%; Al, 8.1%

10.  What are the next five most common elements?

Fe, Ca, Na, K, Mg

Last update 2/25/2005
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