CompuServe Thread

The colour in Agate is similar to the colour in stained glass. The small amount of a metal mixed in with the clear silicate mineral gives it colour. Different metals make different colours. The colours that chemicals like copper sulfate have in solution are similar but the colour that a metal ion gives to a solution will be differnt from the colour that the same metal gives to agate. Colour is caused by the atoms and the bonds between atoms absorbing some wavelengths of light and not others. I hope this is a start please ask for clarification if needed.

Hi, Phil– Welcome to the forum/section! My guess for natural causes of blue in agate would be that traces of copper compounds are present. Chrysocolla (copper silicate) is a copper mineral that could easily be mistaken for quartz (of which agate is a form), and is found mixed into quartz at times. Many other copper minerals are blue, such as turquoise and azurite; it is a characteristic of the copper ion. But my best guess, unless she found it or knows that it was blue when found, is that it has been dyed blue. A lot of agates sold by dealers are dyed, and blue is a less common natural color. –Doug