Chalcedony
Chalcedonies are microcrystallized quartz (translucent but not transparent like rock crystal or amethyst) and without zonations (like agate for example).
The term chalcedony designates this family but also the blue version of this gem. When one wants to speak about another color, one uses their specific name.
chalcedony : blue
carnelian : red-orange
chrysoprase : green
sardony : brown
onyx : black
