21. All delay boxes on the market were quartz crystal accurate by the year 1990. 22. In 1948 researchers at Fort Monmouth grew the first synthetically produced large quartz crystals . 23. The quartz crystal is temperature compensated and is hermetically sealed in an evacuated envelope. 24. Devils Head is most noted for large topaz crystals and even larger smoky quartz crystals . 25. Smoky quartz crystals and topaz are found in many places in the Pikes Peak granite. 26. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes. 27. Many clocks keep time by mechanical resonance in a balance wheel, pendulum, or quartz crystal . 28. Quartz crystals are manufactured for frequencies from a few tens of kilohertz to hundreds of megahertz.29. In modern designs it is common to use quartz crystal filters, especially for narrowband filtering applications. 30. Atomic clocks, which rely on the oscillations of atoms, not quartz crystals , are far more precise.
