Answer:
The essential differences between a diamond and a quartz are in terms of (1) composition (2) structure and crystal form (3) hardness and (4) refractive index.
The diamond is pure carbon in terms of composition whereas the quartz is Silicon dioxide (SiO2). Due differences in internal structures, diamond crystallizes in isometric system, whereas quartz in hexagonal system. The diamond has highest degree of mineral hardness (numbered 10 in Mohs scale of relative hardness) whereas hardness of the quartz is only 7. Similarly the diamond has very high refractive index which is shown as its brilliance and sparkle, whereas quartz does not have such a kind of brilliance.
Further quartz is a ubiquitous mineral formed under low to medium temperature condition, whereas diamond is a less common mineral formed under high temperature and pressure conditions within the earth.
