Quartz.
The mineral that tends to form first in Bowen's series is olivine. It forms at the highest temperatures as cooling magma undergoes fractional crystallization.
The last mineral to form in Bowen's reaction series is quartz. This mineral crystallizes from a melt at lower temperatures, typically below 600 degrees Celsius, after the formation of other minerals like feldspar and mica. Quartz is highly resistant to weathering and is often found in granite and other igneous rocks. Its late crystallization contributes to its abundance in the Earth's crust.
Amethyst is a mineral, a form of quartz.
The mineral form of NaCl is halite. Halite is a common mineral that is often found in sedimentary rocks and in evaporite deposits.
That depends on which form of the mineral. Some minerals have several forms, and the densities vary as the form does.