n the trigonal system. Some of these minerals include hematite, a mineral containing seventy percent iron and has a cherry red color. Calcite, a mineral found in limestone and has colors in the shades of yellow?orange?brown?and green. Siderite, a mineral that is similar to calcite and has a color of pearly gray?yellow?or dark brown. Rhodochrosite?a mineral of calcite cleavage that is translucent with a color of pink. Chabazite, a mineral that almost looks like it crystallizes in the isometric system. Chabazite is translucent and has a white or pink color. Dolomite, it is found in limestone cavities and forms crystals with curved faces. Dolomite is similar to calcite?but harder. Quartz, most common mineral to form crystals and has many different types. Well developed and clear crystals are extremely rare. The color of a quartz is caused by impurities from manganese?iron?and nickel. Some quartz crystals include rose quartz (pink with a tinge of white)?blue quartz (the color is blue and it is the most rare type of quartz)?citrine (yellow)?amethyst (colors range from pastel purple to a dark violet)'smoky quartz (transparent with color of yellow?brown?or black)?and milky quartz (translucent to opaque).
             In the tetragonal system there are three axes. Two of the axes have equal lengths and the other axis has an unequal length. The three axes are right angles to each other. The tetragonal system crystallizes ten percent of minerals?and some of them are autunite, type of uranium mineral that has a pearly green color. Zircon, it is a rare mineral that forms clear?brown colored crystals. Zircon is blue when heated to make gems. scheelite, a glassy'transparent‚and white mineral that is found in quartz. chalcopyrite, a common copper ore that has a brassy?almost gold?color.
             The hexagonal system is somewhat similar to the trigonal system. Like the trigonal system, it has four axes. Thr...