My brittle and prone-to-snagging nails love this, and I never get ragged cuticles anymore.
Recently introduced to the world of "doing your nails"*, I made it my mission to find The Best Thing to file nails and to cut cuticles. I never expected to be using the same product for both tasks !
I dug for information on glass files, cuticle trimmers, and finally stone cuticle erasers. That´s when I found mentions of Ruby Stone crystal nail files, which seem to be a well-kept beauty secret.
Ruby Stone files are nail files and cuticle erasers in one.
As a file, the Ruby Stone is very smooth and doesn´t fray or tear fragile nails. The file is made of synthetic ruby, very hard (9.5 on the hardness scale, 10 being diamond) and the grains are very very fine. Apparently, these fine sharp crystals cut the nails and cuticles instead of tearing them. I tried glass files and seen how much smoother they are in comparison to typical emery boards, well, the ruby files are another big step in smoothness. They won´t give you snags or make your nails peel, and you can file back and forth (Which you should never do with normal emery boards). You can also use them on acrylic nails.
As a cuticle eraser, the Ruby Stone acts like a tiny pumice stone for the cuticles. After cutting away any thick cuticle parts, I use the rounded tip of the Ruby Stone to push back the cuticles and rub them in a kindazig-zag motion. As if I was erasing them. I like to wet my Ruby stone when I do this, it makes everything smoother. I finish by wiping the area with a wet microfibre cloth, and follow it up with my beeswax cuticle conditioner. The result ? My cuticles grow back smooth, not ragged. The first time I had my cuticles done with a cuticle cutter, they grew back horridly ragged. The girl had warned me: once I started cutting them, I´ll have to keep on cutting them for the rest on my life. Ack. I don´t want to be a slave to my cuticles ! Anyway, when I erase them with the ruby stone and finish with the microfibre cloth, they stay smooth. I can do them again at my own leisure.
And the best part ? Like almost all of my fab beauty finds, this one is ridiculously affordable, it comes for around 2$ on Amazon. I got mine on Ebay. There is also the variety with a groove (for long nails), called "Ruby Crystal Ceramic Stone Nail File" which looks like this, but I think that 19$ is a lot to pay for the groove...
The file is advertised never getting dull, but I have seen complaints about the file getting dull with time, I discovered that it is the dead skin and nail cells that settle down between the crystals. When that happens, clean the file with soap and an old toothbrush, and it´s good as new.
Minus points ?
* Ugly, at least the plastic holder thingy at the edge. The glass files are way prettier !
* It takes longer to file the nails. I use the nail scissors, cuticle trimmers and the glass file if there is any quick rough work to be done. The Ruby Stone for the final smoothing.
* They break. Mine fell on the floor and neatly broke in two pieces 
Comparing to a glass file, I´d say that glass is softer but the grains are coarser. The ruby is very hard but very fine. I use glass files if I want to saw down my nail fast, and I´d use it if I had really thick nails. And of course I wouldn´t let the glass anywhere near my cuticles. If you are still using metal files or ordinary emery boards, I recommend at least switching to glass files. They are way kinder to the nails. Oh, and here is another Ruby Stone nail file fan, if you need more convincing.
* In Germany getting your nails done is pretty expensive, so the thrifty do their own.
