Obsidian can be used to recruit the high-tier stone age unitsPitsotl and Eagle Warrior. These units are fairly effective until the mid Copper Age and are relatively cheap to recruit.
While moderately useful, obsidian is not usually considered essential, or actively sought after by experienced players. Adornments require too much obsidian for obsidian outposts to be useful, while obsidian units are only moderately useful for a relatively short amount of time.
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