hydrothermal liquid alteration gives some quartz veinlets rich in those minerals.
Quartz is a mineral that is sometimes in igneous rocks. Quartz can also be found in metamorphic and sedimentary rocks. Rocks are made of minerals that are held together in some way. I'll use jellybeans as an example; if you took a bunch of jellybeans and glued them together into a ball, the ball as a whole would be the rock and the jellybeans would be the minerals. Just as the jelly-rock would have different colors of candy, rocks are made up of different kinds of minerals, one of which is quartz.
Quartz is the crystalline form of the mineral called silica; it is considered a mineral in its own right. Quartz is igneous, because it is produced when molten rock cools.
Mineral generally, but it forms at the interface between igneous intrusion and non-igneous existing layers.
Quartz is a mineral and can form under igneous, metamorphic and hydrothermal events. Quartz can be precipitated directly from magma (igneous) of by silica rich fluids (metamorphic). Quartz is one of the most abundant minerals and can form under many different circumstances.
