It's impossible to definitively say which mineral is the *most* commonly used, as "commonly used" can be interpreted in many ways. It depends on what criteria you're using:

* By weight: If we're talking about the mineral found in the greatest *abundance* in the Earth's crust, it's feldspar.

* By volume: Quartz is the most abundant mineral by volume, making up about 12% of the Earth's crust.

* By economic importance: This is where it gets trickier. Many minerals are essential for different industries, so it depends on what you consider "important". For example, iron is the most used metal, while feldspar is crucial for glass and ceramic production.

* By everyday use: You might argue that quartz is the most commonly used, as it's found in many everyday items like glass, sand, and electronics.

Ultimately, there's no single "most commonly used" mineral. It really depends on how you define "common" and what aspect of use you're focusing on.