Quartz varieties are the safe default. Clear, rose, smoky, amethyst and citrine all handle water, and so does any hard stone with a closed polished surface. The thing to check is what was done to the stone before you bought it.
Fluorite is CaF2, calcium fluoride, and the Handbook of Mineralogy prints that formula with no variants. Keep it in mind next to a line that circulates on lists of stones to keep out of a water bottle: that some fluorite varieties contain fluorine compounds in their structure. The fluorine is in every piece of fluorite that has ever come out of the ground. It is half the mineral.
The sorting is wrong. A list of stones to keep out of a bottle is a list of minerals, and the things that go wrong in a bottle mostly arrived after the mineral did: in a dye bath, or in whatever state the surface was left in when the polishing stopped.
I own a rainbow fluorite spike, palm-sized, bought online after a long evening of comparing listings. The colour bands spiral up through it instead of running flat around it, which is why I picked that one out of the batch. It will never go in a water bottle, and the fluorine has nothing to do with it.
Dye, wax, and the things a bottle finds
Lapis lazuli, the deep blue rock people reach for when they want the bottle to look like something, is the clean case.
GIA’s care page for it describes a chain of treatments. Lapis “that hasn’t been dyed might be impregnated with wax or oil to improve its color and luster.” Where it has been dyed, “the dye used in some lapis can come off if it’s rubbed with acetone (nail polish remover) or denatured alcohol, so it’s sometimes sealed with wax or plastic.” And the seal has a limit of its own: “wax sealers can deteriorate when they’re exposed to heat or solvents.”
Read that as a list of conditions, then think about where a water bottle spends its day. It is wet for hours, warm on a car seat and cold in a fridge within the same afternoon, and it gets knocked against a steel wall every time somebody picks it up. GIA’s cleaning advice for a lapis cabochon, a polished rounded piece with no facets, is warm soapy water and a test on a small inconspicuous area first, “because some dye treatments are not stable”. That is a careful instruction for an object you were about to leave submerged all day.
What follows from ignoring it is undramatic. A stone goes patchy on one side, and the water carries a faint tint you notice on the third refill.
A closed surface and an open one
I have a piece of black tourmaline that would fail in a bottle for a reason no list covers. It is raw, a handful of parallel black columns grown side by side, and it sheds. Set it down on a hard surface and there is black dust around it afterwards. A chip came away onto my finger while I was photographing it, without anything you would call an impact.
Black tourmaline gets recommended for bottles and the mineral earns it. Schorl is hard, seven on the Mohs scale in the Handbook of Mineralogy, and every chip that piece sheds is itself hardness seven. What gives way is the join between one column and the next. Hardness is a property of the mineral, and staying in one piece is a property of the object, and every handful-sized raw black tourmaline I have handled in a shop was a bundle of columns rather than a single prism.
That is the real case for polished over raw. A tumbled or polished stone has been worked until its surface is continuous. A raw piece brings cleavage steps, cavities, grain boundaries and whatever has been sitting in them, and water finds all of it.
The same goes for a polish that was never finished. I keep a white agate sphere, five centimetres across, whose surface carries open crevices and small holes rather than continuous polish. Those crevices are why I like it and not something to look past. They are also exactly the part of a stone that a rinse does not reach, which makes it a fine object and a poor passenger.
Two warnings, and what is behind them
The fluorite line from the top of this piece has a real conclusion hiding under a bad reason. Fluorite is four on the Mohs scale, softer than the steel it would be sharing a bottle with, and a soft stone in a bottle loses its polish and then its edges. Leave it out for that. What you drank does not come into it.
The second warning is about smoky quartz. Some of the smoky quartz on the market got its colour in a gamma cell rather than underground, which good sellers disclose and which unsettles the buyers who read the disclosure. The Health Physics Society took the question directly and answered it in one line: “There is no radiation hazard associated with irradiated smoky quartz.” Their reason is that the photon energy from cobalt-60, which is what the gamma irradiators use, sits below the threshold for the reaction that would make anything radioactive, and it sits below it in every element. A treated smoky quartz is as inert in your water as one that came out of the ground brown.
What the bottle design changes
A bottle with a sealed chamber puts a wall of glass between the water and the stone. Everything above becomes decorative at that point, which is a fact to have before you spend more on the stone than on the bottle. A bottle that takes a loose stone is the one where any of this matters, and it is also the cheaper kind.
The design settles one more thing, which is how much there is to wash. A loose stone adds a surface, a shadow under it, and a second object that comes out wet every time.
Whatever a stone is made of, its page in the Crystalance Mineral Library records it, which beats a list that names varieties without naming minerals. The separate question of which stones dissolve or corrode outright is covered in the care guide on what should not go in water.
Take the stone out when you wash the bottle. Wash both, and let the stone dry before it goes back in.
Sources
- Handbook of Mineralogy, fluorite, for the formula and the hardness: handbookofmineralogy.org
- GIA, Lapis Lazuli Care and Cleaning, for the dyeing, the wax and oil impregnation, the sealers and the cleaning advice: gia.edu
- Handbook of Mineralogy, schorl, for the hardness: handbookofmineralogy.org
- Health Physics Society, Ask the Experts, answered by Mark A. Smith, PhD, CHP, 1 July 2009, for irradiated smoky quartz and the cobalt-60 threshold: hps.org
