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To consider something "alive", couple of conditions exist (according to most definitions today)..
1) responding to external stimuli
2) metabolism
2) replication
4) anything else?
Mules are not a good example.. of course they are alive but can not replicate because they do not have a proper set of genes (in other words, they are sick), so they are sort of "end of line".
Crystals are not alive because they do not have metabolism and do not respond to external stimuli, they do grow but this is not metabolism.
Diatomea is vastly more complex system than anything ever created and/or manufactured by humans, and salt crystals, beautiful to our eyes as they are, are actually very simple structures.
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