The author of the book featured here would like your opinion of this revision of the opening.
Through cracks in the stone, it [What is "it"?] shines like a full moon drenched in blood. [That would take a lot of blood.] [If something is glowing behind cracks, it's more likely to remind you of lightning bolts than a full moon. In fact, if all you see is the light coming through the cracks, it could be a half moon or a sun or a light bulb.] Another strike from my pickaxe exposes the precious crystal. When I pry it loose, it pops out and bounces near the chasm beside the mineshaft.
I dive for the crystal and catch it. I look down. A shiver jolts up my spine, numbing my body with a frozen wave of fear. I’m on the edge of a bottomless pit. [Not crazy about a mineshaft, a chasm and a bottomless pit. Presumably the mineshaft is above, and you came down it to get here, and the chasm is below. And the pit is . . . the chasm?] Helplessly I watch as a chunk of dirt falls until the darkness below consumes it. ["Helplessly" would make more sense if the crystal were falling. He may be helpless to prevent the dirt from falling, but I doubt he cares.] Regaining control of my body, I squirm back, inch by inch, before sinking into the sand and taking a deep sigh. I hate heights. [I would expect a mine to be mostly rock, not sand, especially not in enough quantity to sink into.]
I open my hand and find the crystal cradled in my palm. Unlike diamonds that sparkle in the sunlight, it glows with an unnatural brilliance even here in the darkness. [If this guy's experience with diamonds is from mining them, the ones he's seen probably didn't sparkle much more than a standard rock.] We slaves don’t know why our master wants us to collect them, but these crystals are as precious to us as water.
A forceful tug on my back pulls me up to my feet. It’s my mining partner, RN107. With thick eyebrows and a rigid jaw, he’s got an intimidating face. Like the feathers that fall from a vulture, his hair and beard have faded to a dark gray. [A simile should make something more clear. Hair faded to gray is already clear enough, and even if it weren't, your readers probably haven't seen fallen vulture feathers.]
I'm not sure how much light there is in this mine; you don't want to be describing things you wouldn't see in the darkness. Do they have a light source?
Here's what I would do with this, just to tighten it up:
A blood-red crystal shines through cracks in the mine wall. One more strike from my pickaxe, and it pops out. I dive and grab it . . . and find myself looking into a bottomless chasm. A few pebbles fall, the darkness below consuming them. I squirm back from the edge, inch by inch, then sigh deeply. I hate heights.
I open my hand. The crystal glows with an unnatural brilliance even here in the darkness. We slaves don’t know why our master wants us to collect them, but these crystals are as precious to us as water.
A forceful tug on my back pulls me to my feet. It’s my partner, RN107. With thick eyebrows and a rigid jaw, he’s got an intimidating face, even now that his hair and beard have faded to gray.
I took out about 70 words; if I took some you need, put them back.