I found this chart depicting all kinds of block turquoise available to purchase. Always be aware of what you are buying! I found that gently “tapping” the stone against my teeth is a good test that I can do on site (before purchasing) without damaging the stone. Genuine turquoise will sound like glass when gently tapped against your tooth. Block will sound like plastic. It sounds like a crazy thing to do, but I promise it works!
Block turquoise, sometimes called synthetic turquoise, contains no turquoise at all. It is made by combining inert ingredients, dye, and usually a resin to form blocks that can be cut or shaped. The mixture can also be poured directly into molds to create most any desired shape.