The only real reason to prefer Glass over Quartz (which is also employing silca as the mediumistic conduit) is artistic glass often has lead artficially forced in it to enhance it's properties. Quartz is about 99% silicon dioxide, and glass is generally about 32%. Nothing called "glass" can have more than 80% silicon dioxide, which means you get less puritites, and thus you have an inconsistent molecular structure in cut glass pieces, resulting in greater fragility, heat sensitivity, and imbalance. Glass is an amorphis molten solid, and does not have a true liquid state.
If you do not think there is anything to this, but what is "in you", there is no reason to prefer any to the other, except that a piece could look balanced and not have true balance. Metal is truly the way to go in my opinion, and I would opt for silver or gold. To me, there is part of it that is "in you" but the trappings you emply do matter, WHEN you tap into that. A person who can unlock their own "divine providence" is better off with a thumbtack and a string than a person who is unable to tap into themselves using a machine precise PURE gold pendulum.
Quartz, Sapphire, Emerald, Ruby, and Diamond all suffice but be sure to test weight and balance. Obsidian is the best of the Quartz Family, in my experience, specifically "Snowflake Obsidian." I use large tear-drop shaped Snowflake Obsidian on a silver chain bolted through it's top and to the core. Technically, this is a naturally occuring glass with "spherulites" in it, each housing a crystal. The natural markings make it easy to note rotations. It is machine precise in weight and balance.
I also have a Gold one, but that one is special and only used for specific things.
If this one "spoke" to you, then by all means work with it, and get to know the ropes. Don't be suprised if you grow fast, there comes a time where you can bear more light, and this one seems not able to handle your full energetic capacity. That is probably the point where the impurities will matter. I am of a mind when a divination system speaks to you, it is a sign you are finding a new way to interact with the Higher and Lower planes. Good Luck!