Manufactured quartz slabs are composed of three main ingredients: particles of mineral quartz, resins, and pigments. The quartz particles can vary in size from about 5 millimeters down to less than half a millimeter. Polyester resin binds the mineral pieces together. In some cases, the resin is mixed uniformly through the slab, and in other cases there are visible areas of resin, depending on the design. The same is true of pigments; some designs are the same color all the way through, while others have ribbons or accents of different hues, which are often meant to imitate the naturally occurring patterns in natural stone.
Manufactured quartz slabs are made by blending the ingredients, then pouring the mixture into a mold. Different manufacturers use different processes, but some combination of vibration, compaction, heat, and a vacuum are applied to cure the slabs from a slurry to a solid.
Quartz countertops may include greater or lesser quantities of actual quartz, but they include no solid quartz and likely have lots of other materials in them, as well.
Because quartz is man-made, it can be a less expensive option than quartzite for large, complicated jobs. However, it is not as heat or scratch resistant, and this makes a big difference in how the material performs in the kitchen.
Quartz comes in several color options, because pretty much any color pigment you want can be added in when the material is being made, so you can find quartz that looks fairly natural, like a real piece of stone would, or some that looks colorful and trendy, with obviously unnatural coloring designed to make a statement.