The Four Diamonds
Items Needed: Coins, Charcoal, Blood Rune, 6 Molten Glass (can be noted), 12 Magic Logs (can be noted), 6 Steel Bars (can be noted), bones, ashes, Waterskins ([i]recommended)
Head to the Bedabin Camp in the Kharidian Desert and talk to the Archaeologist near the carpet. Ask him about quests, and he will ask you to take some etchings to the Archaeological Expert at the Exam Center south of the Dig Site.
Head there and talk to the Expert about Desert Treasure. He will give you a rough translation of it. Talk to him again and he will give you the translation. Return to the Archaeologist in the desert and give it to him.
He will take the book, and ask if you want to read it or not. Talk to him again and he will hypothetically make an offer with you on this hypothetical treasure, should it be hypothetically found.
Agree to help him, and he'll ask you to head south to the Bandit Camp. Make sure you aren't wearing any god items! Head into the bar and talk to the bartender. Buy a drink from him then talk to him again and ask about four diamonds.
He will tell you to go talk to someone else. Head into the eastern most building and talk to Eblis. Ask about the four diamonds of Azzanadra. He will tell you that they were stolen by warriors of the false god Zamorak generations ago, and that when you find the warriors, you find the diamonds.
Each diamond has an elemental quality: Blood, Ice, Smoke, and Shadow. He will offer to use a spell, given the right supplies, to help give an idea of where the warriors are. Agree to get the ingredients, then use each of the items on him. (Be careful not to bury the bones!).
Talk to him again and he will tell you to meet him east in the desert. Head to the southeast a little bit and look for him on a hill with a 6 mirrors. Talk to him then look into each of the mirrors.
You can obtain the diamonds in any order you wish.
Diamond of Blood
Items Needed: Garlic, Silver Bar, Pestle and Mortar, Spice
Go to Canifis and heard towards the bar. As you enter, a cut-scene will play. Malak will eventually point you out. Talk to him and tell him you are there looking for a special diamond. He asks that you kill the owner of the diamond, and he will let you keep it.
He tells you that the owner of the diamond is Dessous. Ask where he is at, then ask how to kill him. After talking with him, head to Draynor Village and look for either entrance to the sewers.
In the sewers, look for Ruantun in his makeshift camp. Talk to him and he will make you a silver pot. Now go to Port Sarim and take the boat to Entrana. Head into the large chapel building and speak to the High Priest. Return to Malak in Canifis now, and he will get you some fresh blood.
Grind your garlic and put it in the pot of blood, then add the spice. Kick out the combat gear and prepare for the fight! Dessous is weak to wind attacks, and he uses melee and a magic-based ranged attack. If you try to run around, he will teleport next to you. If he teleports too many times, he will give up and you have to get more blood from Malak.
Head towards the Graveyard to the south when ready.
Use your pot of blood on the large vampire tomb in the middle of the graveyard. To start the fight. Kill him, but he won't drop the diamond! Return to Malak, and he will give it to you.
Diamond of Ice
Items Needed: Climbing Boots, Spiked Boots (take climbing boots + iron bar to Dunstan in Burthorpe), Cake, Restore Potions (highly recommended)
Head northwest of Trollheim, heading towards the ice area. Look for a troll child there. He will be crying, so use a cake on him. (Careful not to eat!) Talk to him again and he will agree to give you the diamond in exchange for freeing his frozified parents.
Note: Once you go through the ice gate, you will be dealt damage from the cold, and your stats will constantly be lowered. You also won't have any run energy.
Squeeze through the ice gate and kill about five or six of the other ice trolls to clear the cave entrance to the east. Follow the path around, past the wolves, until you hit an open area. Kamil will appear and attack you. He is weak to fire, and uses melee and magic that freezes you.
He won't drop the diamond, but continue west. Look for a path going north, and follow it around. You will have to wear your spiked boots here. Once you're all the way around on the east side of the mountain, you will have to climb up onto an ice path. Follow the ice path to the top, then squeeze through the ice gate and cross the bridge.
Right click to smash the ice blocks that the trolls are in, then talk to them. They will take you back to the troll child, and he will give you the diamond.
Diamond of Smoke
Items Needed: Facemask, Rope, Tinderbox, Ice Gloves (required if wielding a weapon), Energy Potions (recommended)
Go to the smokey well west of Pollnivneach and use your rope on the well if you haven't yet. Make sure the facemask is equipped and head down. This dungeon is split into two halves. The eastern half can only be reached by a path on the north. In the east is a room where Fareed is. In the middle of the dungeon is a chest with the key to enter.
But, the chest is locked. To unlock it, you might use your tinderbox on the four standing torches - one is in each corner of the dungeon. You must light them all then reach the chest before they go out. They only stay lit for a short period of time, so it's required to run most of the way (therefore, energy potions are helpful).
It is recommended to start at the southeast corner of the dungeon. With the key in tow, head to the large room on the east side. Fareed will appear when you enter. He is weak to water spells and ice arrows, and primarily uses melee, though can use a little bit of magic if you're standing next to him.
You will automatically pick up the diamond.
Diamond of Shadow
Items Needed: Lockpicks, Waterskins (recommended)
Look for Rasolo the Wandering Merchant in the area marked on the map above, and ask him about the Diamonds of Azzanadra. He has a ring of visibility that he will trade you for a gilded cross that resides in the desert Bandit Camp.
Bring as many lockpicks as you can, and head to the southern tent in the Bandit Camp. Look for the chest and attempt to pick the lock. If you're unlucky, it could take over 100 attempts (and over 100 picklocks!). Just keep trying.
After you get it, return to Rasolo and give it to him. As promised, you will receive the ring of visibility. Put the ring on, and head into the area to the east that is closed off and surrounded by picnic benches. A ladder will appear.
Damis is all the way to the east. Once climbing down, head straight east, then all the way north. Head east, then in the fork in the road, go all the way south. Head east, then you should be able to go into the larger cavern from there.
Run around until Damis appears. There is a safe spot to the north, if you can manage to get him over there. He has two forms, and attacks with melee. He is weak to Iban Blast or Earth spells. His second form hits a lot harder, and drains prayer with each hit.
Kill him and pick up the diamond.
Items Needed: All four diamonds, waterskins (recommended), antiposion (recommended)
Return to Eblis at the mirrors with the diamonds. He will tell you to head to the pyramid to the south and place the diamonds on the obelisks surrounding the pyramid. You can tell which diamond to place based on the color.
After placing all the diamonds, you can now enter the pyramid from the very top. The pyramid contains four floors. Each floor is filled with traps, mummies, and scarab swarms. The swarms can poison you, so beware.
The traps randomly activate, and you will be brought out the back side of the pyramid. Simply go back to the top and retry. Once you reach the final room, speak to Azzanadra. He will ask you about things that you have no clue about.