Can you make shuriken out of obsidian? I would think not, as there wouldn't be any downsides that I can see. They'd just be cheaper and lighter. But I just wanted to make sure.
Price 850 GP
Weight 55 lbs.
This black volcanic glass is extremely sharp, and can be shaped into a variety of weapons that deal piercing and slashing damage. Bits of obsidian inserted into a length of tempered wood create effective swords called terbutjes.
Obsidian weapons cost half as much as base items of their type, and weigh 75% of what base items of their type do.
Obsidian can be used to craft light and one-handed weapons that deal piercing or slashing damage, as well as spear tips and arrowheads.
Obsidian weapons have half the hardness of their base weapons and have the fragile quality.
The fragile glass nature of obsidian is perfect for creating sharp points and blades, but those same qualities make it unsuitable for creating armor. Armor cannot be constructed from obsidian. Magically strengthened obsidian does not have the fragile quality, and can be made into any armor or weapon that can be made of stone.
Emphasis mine.
It is explicitly stated what weapons can be made of obsidian. Shuriken are ranged weapons, not light weapons, one-handed weapons, spear tips, or arrow heads, therefore they cannot be made of obsidian.
None that I can see either. Since they are treated as ammo, the fragile doesn't really come into play, so I'd say go for it. They'd even be rather well suited to it, considering that obsidian can be wicked sharp naturally.
Not shurikens, since they are not light or one-handed.
You can make arrows, but then you might just make them from stone, to make them even cheaper.
But then again, rationally every light and one-handed weapon would be made from obsidian or stone, whether you care for the weight or not. Getting a cheaper weapon, that isn't fragile if it is masterwork.
Making obsidian shuriken would be really hard the flak8ng process if even possible woould make each one a work of art.
Hero Lab tends to play fast and loose with special materials. RAW doesn't allow obsidian shuriken, though I don't really see a good reason why not. You can certainly make obsidian arrows without any downside--apart from ready access to obsidian, I suppose, but that's a GM fiat thing.
On reading further (missed that light weapons/ammo thing entirely), I would still say yes to obsidian shuriken, but there would be a drawback. Since they are lighter and such a tiny weapon to begin with, they would be more difficult to throw accurately at any distance. I would therefore increase the range penalties by 1.