The formatting might still be improved, but here's the info dump for ya. These are from Pristine Quality shards.
Magic+Magic Sorcerer's Gem +1 all unlocked Sorcery skills
Magic+Lightning Gem of Abatement -20% Mana Cost
Magic+Fire Gem of Abatement -20% Mana Cost
Magic+Ice Gem of Abatement -20% Mana Cost
Magic+Physical Warrior's Gem +1 all unlocked Might skills
Magic+Protection Gem of Enlightenment +1 to all first four tier skills
in all trees
Magic+Poison Rogue's Gem +1 all unlocked Finesse skills
Lightning+Lightning Gem of Tempest's Vengence 75% chance to shock enemies when Attacked
Lightning+Ice Gem of Magic Resonance +20% Lightning, Fire, and Ice
damage
Lightning+Physical Gem of Opulence +20% gold drops
Lightning+Fire Gem of Magic Resonance +20% Lightning, Fire, and Ice
damage
Lightning+Protection Gem of the Assiduous +8% more experience
Lightning+Poison Gem of Unrivaled Vitality +50 HP and MP
Ice+Ice Gem of Winter's Vengeance 75% chance to freeze enemies when Attacked
Ice+Physical Gem of Opulence +20% gold drops
Ice+Fire Gem of Magic Resonance +20% Lightning, Fire, and Ice damage
Ice+Protection Gem of the Assiduous +8% more experience
Ice+Poison Gem of Unrivaled Vitality +50 HP and MP
Physical+Physical Gem of the Subjugator +15% Damage and +10% damage
resistance
Physical+Fire Gem of Opulence +20% gold drops
Physical+Protection Gem of the Enlightened +10% experience
Physical+Poison Gem of Opulence +20% gold drops
Fire+Fire Gem of Summer's Vengeance 75% chance to burn enemies when Attacked
Fire+Protection Gem of the Assiduous +8% more experience
Fire+Poison Gem of Unrivaled Vitality +50 HP and MP
Protection+Protection Gem of Paralyzing Vengeance 60% chance to stun enemies when Attacked
Protection+Poison Gem of the Assiduous +8% more experience
Poison+Poison Gem of Plague's Vengeance 75% chance to poison enemies when Attacked
Best Answer
Shards effectively have quality levels. Instead of adding more ingredients like Alchemy and Blacksmithing, increasing one's Sagecrafting skill allows for the use of more advanced shards.
Sagecraft by the Numbers
Three quality levels:
Seven shard types:
Four gem categories:
Skill Progression
All characters can combine Cloudy Shards into gems innately. At level 2, you can combine Lambent Shards into gems. At level 6, you can use Pristine Shards.
Reaching level 3 in Sagecrafting lets you fuse identical shards into a higher tier, much like Diablo II's Horadric Cube, or Torchlight's Transmuter.
Reaching level 8 unlocks the epic gems recipe category.
Reaching Level 10 allows a master Sagecrafter to extract gems from equipment, with no harm to either gem or armament.
Every time you increase your Sagecrafting skill you also increase the chance of finding shards in the first place.
Gem Recipes
Like Alchemy, there are set combinations to create certain effects. Unlike Alchemy, you get a preview of the results of the transmutation before performing it, so you're never sagecrafting blindly.
There are 196 different combinations (7 shard types, 2 shards per gem, 4 categories), but there is some overlap; For instance, Fire + Protection and Ice + Protection both give + Physical Damage when used as a weapon gem.