While still in the water from collecting the previous Lumenspar, swim through the passage here, and past a Dendro Slime. Keep following the passage and a Geovishap will break through the rock. Defeat it and continue through until you reach a pink wall. You need to have leveled your Lumenstone Adjuvant to level 6 to break through it and grab the Lumenspar, though.
Warp to the Teleport Waypoint above The Chasm: Main Mining Area text on the map. Walk northwest up the stairs and past the Oozing Concentrations until you reach the end of the platform. Drop off onto another platform below to find the Lumenspar.
From the same Teleport Waypoint as before, walk up the stairs to the Oozing Concentrations. Go to the rail to the left of the goo and look out across to the long wooden platform on the other side where you'll see the Lumenspar sitting under a hanging lantern. Glide over and grab it.
To get Lumenspar #6, you need to have obtained two Treasure Map Fragments from The Chasm and the Underground Mines.
For the first one, head to Lumberpick Valley in The Chasm in Liyue. Head to the Treasure Hoarder camp in the western section. Defeat the enemies and then check the satchels under the hut to find it.
For the second, head back to The Chasm Underground Mines. Warp to the Teleport Waypoint near Jinwu and then take the eastern path. Go up the ladder and continue on past a Treasure Hoarder camp until you come across a second Treasure Hoarder camp. Take out the enemies and then check the hut's left post to find it.
When you have the two Treasure Map Fragments, warp to the Teleport Waypoint by Tiangong Gorge in The Chasm. Head southeast from here to another Treasure Hoarder camp.
Defeat the enemies and then open the chest. Once it disappears, you'll see a trap door. Go through it to enter a locked room in the Underground Mines with a Precious Chest, Exquisite Chest, and the Lumenspar.
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