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It can be used in a Furnace as effective fuel and can smelt more than a stack. However, this is not recommended as the individual crafting ingredients can smelt 176 items (including the items used to make the Fire Charges; when considering the partial materials used in the two extra Fire Charges, this ends up actually being 162.67 items smeltable), while the Lava Crystal can smelt 132. This assumes you would have made the Fire Charges from scratch and not found them or the Blaze Powder somewhere.
Of course, if used for auto-smelt on a pickaxe, this can end up smelting a potentially infinite amount of ore or logs.