Structure: Iron and magnesium atoms are cations (positively charged). The tetrahedron is an anion, with its overall -4 charge. The tetrahedra are bonded to the iron and magnesium atoms because of the way the octet rule can be satisfied. The tetrahedra are totally isolated from one another, as the iron and magnesium atoms take up the space between the tetrahedra, where they form bonds with the tetrahedra.
Hammer behavior: When struck with a hammer, olivine fractures conchoidally (with curved fractures, as seen in a broken coke bottle). This reflects the evenness of the strength of bonds in olivine, where there aren't planes of weakness along which the hammer blow could produce shear faces (cleavage faces).
Occurrence: forms much of volume of Earth's mantle; found in mafic (iron and magnesium rich) igneous rocks; also in moon rocks, Mars rocks, meteorites.
Structure: single chains of tetrahedra bonded together with magnesium and iron atoms.
Luster: fairly dull, although some vitreous specimens give the name augite, which in Greek means "brightness"
Occurrence: mainly found in mafic igneous rocks, but is found more generally as an accessory mineral in igneous rocks; also common in certain types of metamorphic rocks.
Structure: sheets of tetrahedra, with sheets sandwiched together with bonds to potassium, magnesium, iron, and aluminum atoms.
Hammer behavior: You don't even need a hammer; usually you can peel thin cleavage sheets with your fingernails (these aren't individual sheets, as atoms are tiny!).
Structure: sheets of tetrahedra, with sheets sandwiched together with bonds to potassium and aluminum atoms.
Hammer behavior: Bonds are strong within the framework, but in some planes there are weaker bonds, leading to cleavage at 90 degrees. Orthoclase tends to break into blocky specimens. There are two directions of cleavage, not three. Look at a cardboard box and observe that if you put your hand on top of the box, that is the same plane as the bottom of the box. Take a pen or marker and place a check on the top and bottom of the box. Now move your hand from the top of the box to one of the sides; there is an opposite side of the box that is also in the same plane. Place a check on these two sides. Now, as you move the box around, you will see that there are two unmarked sides. If you look at specimens of orthoclase, you may find cleavage angles at 90 degrees between any two cleavage planes, but like the cardboard box, when you look at the "ends" relative to those two planes, you will not see cleavage. The specimen will not show super smooth surfaces here, and will show uneven fracture.
Hammer behavior: Bonds in the framework of quartz are strong in all directions, so when hit with a hammer, even if the specimen is a beautiful crystal, it just fractures conchoidally.
Hammer behavior: Talc is very soft, so it comes apart into pieces easily. Technically, there is a perfect direction of cleavage when you can see it.
Hammer behavior: Kaolinite is very soft, so it comes apart into blocky, irregular pieces easily.
Hammer behavior: See comment above; in microscopic view, can see good cleavage in one direction.