Granite is high in quartz, a mineral very resistant to weathering. Similarly, quartzite is harder than steel. So, they are not easily worn down and give rise to upstanding mountains and hills (Environmental Biology by P.D. Sharma, p. 37). However, they are subject to differential weathering: a rock that is resistant in a climate dominated by chemical weathering may be weak where physical weathering process dominate, and vice versa. So quartzite, though hard and chemically inert, can be fractured by physical weathering. Similarly, granite outcrops in arid or semi-arid region resist weathering; however, the minerals in granite are susceptible to alteration by oxidation, hydration and hydrolysis, particularly in regions with warm, humid conditions (Essentials of Physical Geography by Robert Gabler, James Petersen, L. Trapasso, p. 34).