Some are ancient, some contemporary. A few have been made from pure quartz and are absolutely clear. A rare few are also life-sized. Quartz, composed almost entirely of silicon dioxide, is found in almost every type of rock and can form huge crystals that weigh tons. While it is colorless and transparent when pure, when a tiny portion of the silicon atoms are replaced with iron, aluminum, manganese or titanium, the crystal can take on beautiful colors.
Amethyst is violet quartz.
Jasper is quartz with red, yellow, brown, gray or black coloring. Onyx and Agate are quartz with bans of color. Bloodstone is green with red spots. If a single streak runs through the quartz it might be called Cat's Eye, Tiger's Eye or Rutile . All crystal is ancient and there are no good ways of guessing how long ago a skull shape was carved or polished out of the quartz.