Quartz is not formed from other rocks. It's a mineral, not a rock. Rocks are made up of multiple minerals.

Quartz is formed through crystallization from magma (molten rock) or lava, or through precipitation from water solutions.

Here's a breakdown:

* Magmatic/Igneous Quartz: Quartz crystallizes directly from cooling magma or lava.

* Hydrothermal Quartz: Quartz forms from hot, mineral-rich water solutions.

* Sedimentary Quartz: Quartz can also be found in sedimentary rocks formed from weathered and eroded rocks. However, the original quartz crystals themselves weren't formed within the sedimentary rock; they were simply transported and deposited there.

So, while quartz can be found in different types of rocks, it's not formed *from* them. It's a fundamental component of many rocks, but it forms through its own processes.