Here is the best off the cuff extrapolation I can give you:

Given that there is no indication (that I can find) that any dragonshards are in particular different hardness or hp from each other regardless of type, comparing the two example shards and doing the math gives us a base hardness of 10 and a base hp of 15 per inch of thickness.

While magic weapons and armor increase in hardness and hp based on the +1 through +5 stat, other magic items don't seem to give any guidelines. However, I have seen it elsewhere proposed, and find it perfectly reasonable to take the caster level required for the +1 through +5, and apply the same increase in hardness and hp based on the caster level required to create said wondrous item; since they are the most likely to fail to list a hardness or break dc.

Or you could simplify it and not bother with the per-item thing and simply say that minor is equivalent to +1, medium to +3, and major to +5.

As for the lantern, it would have the same break dc and hardness as a regular bull's eye lantern, unless you wish to consider the entire package, the wondrous item. If you can't find stats for that, given the effective thinness of the metal used in a lantern, the hardness and break dc won't be that high. As you would do the calculation per inch in reverse. It might survive a fall from a shelf, so maybe a hardness of 3 to 5, and maybe 1 to 3 hp.

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