Amethyst Geode with Rich Purple Colour
A free-standing amethyst geode with small, translucent crystals.
A geode is a rock with a hollow cavity in which crystals have grown slowly over millions of years. These cavities form in volcanic or sedimentary rocks. Over time, mineral-rich groundwater seeps into the space. As dissolved minerals are deposited, crystals begin to grow.
This process can continue for millions of years. The amethyst crystals may be smaller if growth stopped earlier, usually because the supply of mineral-rich water decreased or stopped completely. When the flow of dissolved minerals stops, so does crystal growth.
The first crystals to form are usually clear or milky quartz. They're white because they lack the trace elements needed to produce colour.
Trace amounts of iron within the quartz, combined with natural radiation from surrounding rocks, produce the purple colour. Where insufficient iron is present, the quartz remains white, or the shade of purple is less intense.
