There is something undeniably magical about finding a crystal with a moving bubble inside, it feels like something that should be impossible when you see one for the first time. These crystals are most commonly referred to as ‘enhydros’, although there are actually distinct differences between an enhydro and the less commonly known ‘fluid inclusion’.
The term ‘enhydro’ should be limited to the chalcedony (most commonly referred to as ‘Agate’) geodes or nodules, mainly found in Brazil, which contain cavities filled with water and air bubbles. These geodes are very slightly porous, which means water can enter and exit the geode, albeit incredibly slowly, so that the water that may seep into a geode over a period of many many years is not necessarily the same water that was present when the geode was formed. This also leaves open the possibility for these enhydro geodes to slowly dry out over time and to lose their ‘bubble’ - when you see them for sale at tradeshows, they will often be immersed in large buckets of water to preserve the ‘bubble’.
Fluid inclusions, on the other hand, are formed at the same time as the crystal, and should be in little to no danger of evaporating, unless damage was done to the crystal when it was excavated. When a crystal is growing, the different faces and sides of a crystal can grow at different rates, so tiny pits can occur in the crystal, and the crystal will continue to grow over these, enclosing them and creating the chamber for the bubble in which to form. The hot, silica rich ground water in which these crystals are growing, then cools inside the chamber, and contracts, reducing in size and so shrinks, pulling away from the walls of it’s tiny chamber and creating a vapour bubble, which is what we can see moving when we shake the crystal.
Although Quartz varieties are the most well known crystal for fluid inclusions, they can occur in a variety of other crystals - Selenite, Halite, Fluorite, Aquamarine and many more. These fluid inclusions are not always water, they can also contain carbon, oil, liquid CO2 and more. Fluid inclusions are also notoriously volatile - they are prone to explosion at very hot or freezing temperature! Just as the liquid inside them cooled and contracted to form the bubble in the first place, if this same liquid heats up too much, or freezes (such as left outside overnight in freezing temperatures), then the liquid and gas inside expands again, running out of room and bursting the crystal. This has been known to happen under the very bright, hot lights of a gem show display case, but is much less likely to occur at home under the softer LED lights that are now more commonly used. As fluid inclusion is a much less well known term than enhydro, we tend to refer to our various fluid inclusions crystals like Brandbergs, Quartz etc as enhydro so people are more aware of what we’re talking about, but these are technically fluid inclusions.
There has been much fascination with these “water crystals” over the years, in the first century AD the Roman Court Poet Claudin wrote a series of short poems about enhydro crystals, who’s title translates roughly to ‘On a crystal which contains water’. This is the second one of seven, translation taken from thepetrifiedmuse.blog:
Waters, covering waters in kindred prison-cell,
both you that still are, and you that once were, liquid:
what genius united you? By what trick of freezing
is the marvellous stone both hard and wet?
Which gentle heat, locked in, governs the protected welters?
What southern breeze turned a frosty core liquid again?
What caused the gemstone, moving by some hidden surge,
to be solid or free from frost
The full translation can be found here: https://thepetrifiedmuse.blog/2017/02/05/hard-shell-soft-core/