Enhydros
Sometimes a Quartz crystal will have a little pocket inside it, with liquid that moves around. You rock it side to side to watch the bubble move up and down and it is usually mesmerizing. These are often called enhydros. I call them that. Funny thing is- that’s NOT an enhydro! These are actually called fluid inclusions! An enhydro is something else altogether and I’ll get to that soon - I promise!
First, how do these liquid inclusions occur? When the Quartz crystal is forming, often from hot groundwater containing silica, there can be inconsistencies in the layers, where some parts form more quickly than others. In some cases this could cause a small pit to form. This pit, while full of water, is then sealed off when the Quartz continues to form over the pit. This leaves a pocket that is completely full of water.
Next, as the crystal cools, so too does the liquid inside- and both contract (become smaller in volume). The water contracts more than the crystal does, so that the liquid inside the pocket becomes smaller than the pocket itself. The liquid pulls away from the walls of its pocket, forming a little vapor bubble that can move around the pocket.
Vapor bubble formed inside Quartz
Milky Quartz gets it’s white color from tons of microscopic fluid inclusions. How crazy is that?! And the liquid trapped inside a crystal isn’t always just water. When hot saltwater gets trapped inside of Quartz, the salt can crystallize into a tiny Halite crystal! Herkimer diamonds from New York often have fluid inclusions with Carbon in them, which look like black specks. Some Quartz from Pakistan have Petroleum inside them, as well as Fluorites from Elmwood, Tennessee. Liquid inclusions vary so much- and they are tiny time capsules to geologists- a pure sample of the liquids present when the crystal formed!
So what is an enhydro?
An enhydro is defined as “a hollow nodule or geode of chalcedony containing water, sometimes in large amounts.”
Therefore, liquid inside Quartz it is not a true enhydro. Chalcedony is a micro-crystalline variety of Quartz (made up of many microscopic, elongated Quartz crystals), but Quartz is not a Chalcedony. Some varieties of Chalcedony include all Agates, Onyx, and Jaspers. So since Agate is a Chalcedony, that means that Agate geodes that have water trapped in the hollow center ARE in fact, true enhydros. They are probably the only liquid inclusion I know of that do fit the true definition of an enhydro!
Another difference between the two, is that with a liquid inclusion, we talked about how the liquid is forever trapped, and unless opened up that liquid will stay the same as it was the day it was trapped, for all eternity. But in an enhydro, the stone is porous, and the water actually is able to seep in and out of the geode! So the water inside could be from the time just before it was collected, rather than the time the stone itself formed. Once collected, the water can continue to seep out, though very slowly. Some seal them to keep this from happening.
Agate Enhydro Geodes
Now, I know that most folks already call liquid inclusions enhydros regardless of what type of rock they’re in, and that most people don’t know the difference. I’ll have to keep calling them enhydros so that people know what I’m talking about and can find them in my shop. But it’s still a fun bit of knowledge for you to have up there in your noggin!