Here is an update to the info posted earlier, with all related items, and results of clicking the gems:
To obtain this 25-slot bag, one must collect three specific loot cards from the LoN expansion "Legacies" (released 2011-03-02):
Venomous Raptor Saddle (1/3)
Idol of Talendor (2/3)
Flame Wurmling (3/3)
When you claim these, they each come in a container that contains two items: the item itself, and a gem:
Raptor Saddle Package: Contains Venomous Raptor Saddle and Warm Ruby Shard
Worn Red Chest: Contains Idol of Talendor and Warm Garnet Shard
Wurmling Crate: Contains Flame Wurmling and Warm Sapphire Shard
There is some "Item information" printed on each gem's item description window, suggesting that one should right-click it:
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Item information:
Inspect the shard more closely.
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When you have only one gem in inventory, right-clicking it gives:
[Fri Apr 22 04:23:09 2011] The shard quivers and you get the impression this item is part of a set of three. Gather the other two shards to see if there is any reaction.
When you have two gems in inventory, right-clicking either one gives:
[Fri Apr 22 04:23:45 2011] The two shards resonate slightly. Only one more shard remains to be found.
When you have all three gems in inventory, right-clicking any of them gives:
[Fri Apr 22 04:35:41 2011] The three shards resonate and meld together. You are momentarily blinded by a brilliant light. When you are able to see again, you notice a bright red pack where the shards were previously.
Once you have all 3 of the gems, right-click any one of them in your inventory, and they will be replaced by this 25-slot bag on your cursor.
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Rondor