— he sent me three pretty rocks! 😃 I will talk about one of them here and the others in another post.
This beautiful rock has probably been dyed on the outside, as such vibrant blue colors are not often seen in nature (although they are, sometimes). But it is a lovely color, definitely! This is the outside of a geode, a rock with a hollow center in which small crystals have grown by mineral-rich water seeping into it through small cracks. Most geodes have clear quartz crystals inside, but purple amethyst can also be found as well as celestite, calcite, and other minerals.
The following photo shows the view into the vug (the hollow cavity) of this geode, and bright spots of reflected light can be seen. Extremely small crystals such as are found in geodes are called druze (rhymes with "ooze").
Also, with a little imagination, the opening of the vug mimics the outline of a kittycat, so
The following 30-second video shows the geode being slowly turned in my hand, and the play of light off the druzy crystals makes teeny flashes of light, like glitter:
video by me
Geodes come in all sizes — and, as with most things, there are many small ones, but the larger sizes are more rare. Those the size of baseballs are more rare than this size, and softball-sized geodes are more rare still. I found two sources, both of which claim to be the "largest geode in the world" — I can't be certain which source is accurate at truly being the largest, but both are amazing, indeed. The one that, perhaps, is the larger of the two has dimensions up to 35-feet (10.668 m) in diameter and is called Crystal Cave on South Bass Island in Lake Erie, off the shore of Ohio in the US. The other is Pulpí Geode in Southern Spain, described as being "a 390-cubic-foot (11 cubic meters) cavity about the size of a cement mixer drum." [source]
SOURCES
1 Geology.com: Geodes
2 Wikipedia: Geode
12-Nov-2019
