Justin Hi Justin, Those are questions that are probably best answered in an intro geoogy book. Ill try to give you quick answers. The pressure and temperature inside the Earths core are incredibly high. Thats not a super well-known number.
Sound does exist within the earth because sound can go through solids and liquids.
Different parts of the mantle are more like solids whereas other parts are more like slushes. The asthenosphere, for example, which extends from about 100 km down to around 250 -350 km is pretty slushy. When theyre flowing you can only see little bits of incandescence unless there is an open channel. There are numerous photos of lava flows in VolcanoWorld. Some lavas can crystallize quartz crystals.