Final answer:
The gemstone minerals that contain the two most abundant elements by mass in Earth's crust are Quartz and Topaz, since the most abundant elements are oxygen and silicon which are prominent in silicates.
Step-by-step explanation:
The question is asking which gemstone minerals contain the two most abundant elements by mass in Earth's crust. The two most abundant elements are oxygen and silicon.
Considering the information provided, the gemstones that fit this criterion are ruby and sapphire, both varieties of the mineral corundum, which is primarily composed of aluminum and oxygen. However, the silicate minerals are the most abundant in Earth's crust, making up 92%. Quartz, being silicon dioxide (SiO2), fits this criterion as well. Topaz is a silicate mineral of aluminum and fluorine and also contains oxygen in its structure. Therefore, the correct answer is (c) Quartz and Topaz.