Quartzite is metamorphosed from

Answer: (c) Sandstone

Sandstone metamorphoses into quartzite.

The idea

Metamorphism changes an existing rock through heat, pressure and fluids while it remains largely solid. The parent rock controls which minerals are available. A quartz-rich parent can recrystallise into a hard rock with tightly joined quartz grains.

Quartz-rich sediment forms sandstone → Sandstone is buried or heated → Quartz grains recrystallise → Grain boundaries become tightly joined → Quartzite forms without wholesale melting

Why the others are wrong

(a) Limestone becomes marble.

(b) Obsidian is volcanic glass.

(d) Shale becomes slate.

Elimination technique

Quartzite is dominated by quartz, so look for a quartz-rich parent. Sandstone fits; limestone supplies calcite and shale commonly supplies clay minerals.

Also know

Carry the companion pairs: limestone becomes marble, shale can become slate, and granite can become gneiss. Slate commonly develops cleavage, while marble and quartzite usually lack such layering. Contact metamorphism occurs near hot intrusions; regional metamorphism affects broad areas during mountain building.