What is the principal mineral used in making glass?

Glass is manufactured primarily from the mineral quartz (SiO2) which is what sand is made from.

However small amounts of other minerals are added to the sand to make the process easier. These minerals are:-

sodium carbonate (Na2CO3)

lime (calcium oxide (CaO)

magnesium oxide (MgO)

aluminum oxide (Al2O3)

There are also other minerals which are added to make specialised glasses. e.g. Pyrex glass is made from sand and boron oxide.