Short answers, pulled from the story.
Sandstone is a clastic sedimentary rock composed mainly of sand-sized silicate grains, ranging from 0.0625 to 2 millimetres in diameter, bound together by a cementing mineral. Most grains are quartz or feldspar, the minerals most resistant to weathering at the Earth's surface. Common cements include quartz, calcite, hematite, gypsum, and clay minerals.
Sandstone makes up approximately 20-25 percent of all sedimentary rocks.
Sand is buried by younger sediments and undergoes diagenesis, a process of compaction and lithification. Pressure from overlying rock compresses the grains, dissolves material at grain contact points, and drives cementation. Mechanical compaction occurs mainly at depths below 1,000 metres, while chemical compaction and cementation continue to depths of 2,000 metres.
Sandstone formations are porous enough to store large quantities of fluids and permeable enough to allow those fluids to flow through them, making them valuable aquifers and petroleum reservoirs. The porosity and permeability depend on how the grains are packed and how much cement has filled the pore spaces.
Quartzite forms when sandstone is subjected to the high heat and pressure of regional metamorphism, causing the quartz grains and cement to recrystallize. Unlike sandstone, quartzite fractures through the grains rather than around them, and most original sedimentary textures are erased. Orthoquartzite is a sandstone so thoroughly cemented by diagenesis that it resembles metamorphic quartzite but still preserves original textures and fossils.
Red sandstone gets its color from hematite, which is likely formed during eogenesis, the earliest stage of diagenesis that takes place at shallow burial depths of a few tens of metres. The red rock deserts of Arches National Park are a well-known example of this coloration.