NightGems

I wanted something real worldly to represent the NightGems. In fact it is a reverse cause-effect thing, I came up with the Gem first, and then backed up the story all the way to the Fall of the Night.

NightGems are simply obsidian. Volcanic glass.

If you're not prepared for it, it looks like a really unusual stone (it's not uncommon or even that precious). It looks of what it is, glass made by volcanic lava melting the sand and soil around it. It later shatters, like the glass it is. The impurities in the soil turn it dark (from blues to blacks).

Also its edge. Like 'normal' glass, obsidian gets really sharp edges and was used in fact as sacrificial knives by pre-Colombian civilisations, who never really cared for metals.

They come in a variety of grades: Alpha Grade are the worse and cheapest, most impure ones, little more than inert rocks. Gamma Grade are where the real power starts. The newest 4th Gen Core runs on Lambda Grade. Purest forms are being researched, as the shards that created the Passages are named Omega Class. None have ever been found....

NighGems, as I mentioned, are my gimmick for Thyra, a power source our victorians could only dream of. The reason they never developed flight, is that a steam engine is so big and heavy, it is impossible for it to lift itself. But with NightGems? Your engine could be 10 times smaller and 100 times lighter. Now, then, there is some potential here....