Q: What are the stones used in the movement?
A: Synthetic ruby to reduce friction and wear
To reduce friction and wear that occurs between the movement's pivots (tenons) and the bridges or main plate, most mechanical movements (and some high-end quartz movements) use synthetic ruby (or synthetic sapphire) in the bearings. In rare cases, diamonds are used, but because they are too hard and cause wear to the pivots, synthetic ruby is the only stone used today.
Since the development of synthetic ruby manufacturing methods in the first half of the 20th century, the number of jewels used in movements has increased. For a hand-wound mechanical movement, the minimum number of jewels required is seven. However, 17 or more jewels are considered desirable. Specifically, these are the upper and lower jewels of the second wheel (two jewels), the upper and lower jewels of the third wheel (two jewels), the upper and lower jewels of the fourth wheel (two jewels), the upper and lower jewels of the escape wheel (two jewels), the pallet stones on the left and right of the pallet fork (two jewels), the upper and lower jewels of the pallet fork (two jewels), the impulse jewel (one jewel), the upper and lower jewels of the balance fork (two jewels), and the upper and lower jewels of the shock-resistant device (two jewels).
Incidentally, some inexpensive quartz movements do not have jewels. In theory, these will not last long. Furthermore, the number of jewels increases as the number of functions increases. For example, many complicated watches have more than 100 jewels.
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