Easiest first step is lick it to see if you stick!
That's chalk, and about all you can do is stabilize it.
After that, you will get so many thoughts and opinions the best you can do is pick and choose which advice you like, give it a try, and see what you want to do after that.
A lot of people believe in stabilization whether the turquoise needs it or not. I get the theory- that way it will never change color. Turquoise often goes a brown/green over the decades as it absorbs the air and oils from it's surroundings. But then again that green patina is valued. Really, really good gem grade turquoise should stay the same regardless of time.
So for me, here's my thoughts. If it is chalk either stabilize it or put it in your garden for some lovely color. If it doesn't stick to your tongue, try cutting some. If it cuts well and doesn't break up then you have a lovely natural stone which is worth volumes more than if you stabilized it. If it is gem grade and takes a great polish, then you have something of value. If not, the value is relative, but for natural it can be surprisingly pricey. Do you know which mine it came from?
As for stabilizing, PhilNM has done lots of turquoise stabilizing. He would probably be your best bet for information. But from what I have read, and tried myself, you do it about exactly the same way you do any other material. Several options, but they are pretty much the same from material to material. Good luck!
