Quartz is used in the glass, calcite is used to purify the glass; hematite or aluminum is used in the frame and lock mechanism.
the most recent was mount Helena in 1980
It was cold and there were 2-3 ice ages. The woolly mammoth, woolly rhino, and other extinct animals evolved in this period. it is divided into two periods, the Pleistocene which is the ice age and the Holocene or the present time. the hippo was one of the many animals to survive this age. other animals such as the elephant and rhinoceroses also survived. This period started about 2.6 million years ago. On the time line this is just a scratch.
Zero degrees! If the angle of declination is 0°, then magnetic north is exactly the same as true north, making it much easier to navigate. But really, there isn't any "optimum" angle. One angle is just as good as another as long as you know how to correct for it in the right way.