Answer:
a) The mineral Quartz (silicon dioxide SiO2), is created by combining the elements silicon and oxygen.
b) Coal, from plant materials, and limestone (calcium carbonate CaCO3) created by corals and other sea creatures, are not minerals even though they are mined like many ores.
Step-by-step explanation:
Quartz is a very hard mineral created by combining the elements silicon and oxygen. It is chemically stable and so weathers very slowly. The quartz crystal can be colored yellow, brown, black, milky white, rose, etc depending on the impurities in the rock at the time of formation. It is used in the production of optical instruments, various electrical devices, sandpaper, grinding tools, etc.
Coal is formed from the gradual accumulation of plant remains (peat) that are found in tropical wetlands. It is used as fuel for electric power generation, in blacksmithing purposes and to make coke.
Limestone is made up of skeletal fragments from marine organisms like corals, planktons, coralline algae, sponges, echinoderms, mollusks, foraminifera, etc. The shells of most of these organisms are made up of aragonite or calcite. When they die, the shells left behind are accumulated over millions of years and form limestone. It is used in the production of lime, used as a building material and filler in products like toothpaste or paints. It is also an essential component of Portland cement.