Quartz is a dense crystalline mineral. It is composed of silicon dioxide. It is formed through igneous rocks or geothermal waters. In igneous rocks it occurs when magma cools and silicon dioxide will crystalize. In silicon dioxide rich waters as from the mineral being dissolved in high temperatures. When the water cools or pressure drops the mineral is saturated forming crystals.
There are many kinds of quartz. These can include semi-precious gemstones. They have been used to make jewelry. It is also the second most available crystal on Earth.
Heinrich Cornelius Agrippa in his Three Books of Occult Philosophy associates this crystal to the Moon: https://logosofophiel.com/2021/07/03/renaissance-magic-of-the-moon/