Ore Geodes

Adds a small but still interesting change to caves - ore geodes!
They resemble amethyst geodes in appearance, but instead of the usual layers, their interior is made of stone infused with single-block ore or stone veins.

The more valuable the resource inside a geode, the deeper and less common it is.

Discovering an ore geode feels like a surprise - you never know what might be inside. Many geodes may turn out to be empty, containing only stone rather than valuable resources.