The four minerals shown above (Rock Crystal, Rose Quartz, Amethyst and Carnelian) are all Quartz. The presence of small amounts of varying chemical agents in the environment around them change the colors and properties of the mineral.
A mineral which has fully formed can also become a completely different mineral if exposed to light and/or heat as shown below.
The mineral angelite /anhydrite (CaSO4) becomes gypsum (CaSO4.2H2O) when water is added via hydration. The reverse process occurs if gypsum is dehydrated.