diff --git a/.luacheckrc b/.luacheckrc
index 29d0418..319eba3 100644
--- a/.luacheckrc
+++ b/.luacheckrc
@@ -30,5 +30,6 @@ read_globals = {
 	"vector",
 	"VoxelArea",
 	"VoxelManip",
+	xpanes = { fields = { "register_pane" } },
 }
 
diff --git a/README.md b/README.md
index 3f20e49..1291f5c 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,8 @@ SOFTWARE.
  * `nether_book_`* (files starting with "nether_book"): Treer, 2019-2020
  * `nether_brick_deep.png`: Treer, 2021
  * `nether_fumarole.ogg`: Treer, 2020
+ * `nether_geode.png`: Treer, 2021
+ * `nether_geode_glass.png`: Treer, 2021
  * `nether_lava_bubble`* (files starting with "nether_lava_bubble"): Treer, 2020
  * `nether_lava_crust_animated.png`: Treer, 2019-2020
  * `nether_lightstaff.png`: Treer, 2021
diff --git a/depends.txt b/depends.txt
index 2ccaf36..93b4329 100644
--- a/depends.txt
+++ b/depends.txt
@@ -7,3 +7,4 @@ loot?
 mesecons?
 moreblocks?
 climate_api?
+xpanes?
\ No newline at end of file
diff --git a/locale/nether.fr.tr b/locale/nether.fr.tr
index 12ce386..2bfbb6c 100644
--- a/locale/nether.fr.tr
+++ b/locale/nether.fr.tr
@@ -64,11 +64,19 @@ Lava Crust=
 Lava crust is strong enough to walk on, but still hot enough to inflict burns.=
 
 Nether Basalt=
+Nether Beryl=
+Nether Berylite=
 Nether Brick=Brique du Nether
 Nether Brick Fence=Barrière en briques du Nether
 Nether Brick Fence Rail=Clôture en briques du Nether
+Nether Crystal Pane=
 Nether Slab=Dalle du Nether
 Nether Stair=Escalier du Nether
+
+Nether geode crystal, found lining the interior walls of Nether geodes=
+
+Nether geode crystal. A crystalline structure with faint glow found inside large Nether geodes=
+
 Netherrack=Roche du Nether
 Netherrack from deep in the mantle=
 Netherrack stair=
diff --git a/locale/template.txt b/locale/template.txt
index fa3d032..018091c 100644
--- a/locale/template.txt
+++ b/locale/template.txt
@@ -63,11 +63,19 @@ Lava Crust=
 Lava crust is strong enough to walk on, but still hot enough to inflict burns.=
 
 Nether Basalt=
+Nether Beryl=
+Nether Berylite=
 Nether Brick=
 Nether Brick Fence=
 Nether Brick Fence Rail=
+Nether Crystal Pane=
 Nether Slab=
 Nether Stair=
+
+Nether geode crystal, found lining the interior walls of Nether geodes=
+
+Nether geode crystal. A crystalline structure with faint glow found inside large Nether geodes=
+
 Netherrack=
 Netherrack from deep in the mantle=
 Netherrack stair=
diff --git a/mapgen.lua b/mapgen.lua
index df82e58..e2316b1 100644
--- a/mapgen.lua
+++ b/mapgen.lua
@@ -71,6 +71,7 @@ end
 -- Load specialty helper functions
 dofile(nether.path .. "/mapgen_dungeons.lua")
 dofile(nether.path .. "/mapgen_mantle.lua")
+dofile(nether.path .. "/mapgen_geodes.lua")
 
 
 -- Misc math functions
@@ -283,6 +284,7 @@ local dbuf = {}
 local c_air              = minetest.get_content_id("air")
 local c_netherrack       = minetest.get_content_id("nether:rack")
 local c_netherrack_deep  = minetest.get_content_id("nether:rack_deep")
+local c_crystaldark      = minetest.get_content_id("nether:geode")
 local c_lavasea_source   = minetest.get_content_id("nether:lava_source") -- same as lava but with staggered animation to look better as an ocean
 local c_lava_crust       = minetest.get_content_id("nether:lava_crust")
 local c_native_mapgen    = minetest.get_content_id("nether:native_mapgen")
@@ -382,7 +384,8 @@ local function on_generated(minp, maxp, seed)
 				if cave_noise > tcave then
 					-- Prime region
 					-- This was the only region in initial versions of the Nether mod.
-					-- It is the only region which portals from the surface will open into.
+					-- It is the only region which portals from the surface will open into,
+					-- getting to any other regions in the Nether will require Shanks' Pony.
 					data[vi] = c_air
 					contains_nether = true
 
@@ -392,12 +395,11 @@ local function on_generated(minp, maxp, seed)
 					-- Reaching here would require the player to first find and journey through the central region,
 					-- as it's always separated from the Prime region by the central region.
 
-					data[vi] = c_netherrack -- For now I've just left this region as solid netherrack instead of air.
+					data[vi] = mapgen.getGeodeInteriorNodeId(x, y, z)-- function from mapgen_geodes.lua
 
 					-- Only set contains_nether to true here if you want tunnels created between the secondary region
 					-- and the central region.
-					--contains_nether = true
-					--data[vi] = c_air
+					contains_nether = true
 				else
 					-- netherrack walls and/or center region/mantle
 					abs_cave_noise = math_abs(cave_noise)
@@ -414,7 +416,11 @@ local function on_generated(minp, maxp, seed)
 								data[vi] = c_netherrack_deep
 							else
 								-- the shell seperating the mantle from the rest of the nether...
-								data[vi] = c_netherrack -- excavate_dungeons() will mostly reverse this inside dungeons
+								if cave_noise > 0 then
+									data[vi] = c_netherrack -- excavate_dungeons() will mostly reverse this inside dungeons
+								else
+									data[vi] = c_crystaldark
+								end
 							end
 						end
 
diff --git a/mapgen_dungeons.lua b/mapgen_dungeons.lua
index 64a73af..ca77ae1 100644
--- a/mapgen_dungeons.lua
+++ b/mapgen_dungeons.lua
@@ -33,6 +33,7 @@ minetest.set_gen_notify({dungeon = true})
 local c_air              = minetest.get_content_id("air")
 local c_netherrack       = minetest.get_content_id("nether:rack")
 local c_netherrack_deep  = minetest.get_content_id("nether:rack_deep")
+local c_crystaldark      = minetest.get_content_id("nether:geode")
 local c_dungeonbrick     = minetest.get_content_id("nether:brick")
 local c_dungeonbrick_alt = minetest.get_content_id("nether:brick_cracked")
 local c_netherbrick_slab = minetest.get_content_id("stairs:slab_nether_brick")
@@ -164,7 +165,7 @@ nether.mapgen.excavate_dungeons = function(data, area, rooms)
 				vi = area:index(room_min.x, y, z)
 				for x = room_min.x, room_max.x do
 					node_id = data[vi]
-					if node_id == c_netherrack or node_id == c_netherrack_deep then data[vi] = c_air end
+					if node_id == c_netherrack or node_id == c_netherrack_deep or node_id == c_crystaldark then data[vi] = c_air end
 					vi = vi + 1
 				end
 			end
@@ -181,7 +182,7 @@ nether.mapgen.excavate_dungeons = function(data, area, rooms)
 				vi = vi + area.ystride
 				node_id = data[vi]
 				-- searching forward of the stairs could also be done
-				if node_id == c_netherrack or node_id == c_netherrack_deep then data[vi] = c_air end
+				if node_id == c_netherrack or node_id == c_netherrack_deep or node_id == c_crystaldark then data[vi] = c_air end
 			end
 		end
 	end
@@ -231,11 +232,11 @@ nether.mapgen.decorate_dungeons = function(data, area, rooms)
 			   and room_min.z > minEdge.z and room_max.z < maxEdge.z then
 				--data[area:indexp(roomInfo)] = minetest.get_content_id("default:mese_post_light") -- debug
 
-				-- Can't use glass panes because they need the param data set.
-				-- Until whisper glass is added, every window will be made of netherbrick fence (rather
-				-- than material depending on room_seed)
+				-- Glass panes can't go in the windows because we aren't setting param data.
+				-- Until a Nether glass is added, every window will be made of netherbrick fence rather
+				-- than material depending on room_seed.
 				local window_node = c_netherfence
-				--if c_netherglass ~= nil and room_seed % 20 >= 12 then window_node = c_crystallight end
+				--if c_netherglass ~= nil and room_seed % 20 >= 12 then window_node = c_netherglass end
 
 				local function placeWindow(vi, viOutsideOffset, windowNo)
 					if is_dungeon_brick(data[vi]) and is_dungeon_brick(data[vi + yStride]) then
diff --git a/mapgen_geodes.lua b/mapgen_geodes.lua
new file mode 100644
index 0000000..810e19e
--- /dev/null
+++ b/mapgen_geodes.lua
@@ -0,0 +1,221 @@
+--[[
+
+  Nether mod for minetest
+
+  This file contains helper functions for generating geode interiors,
+  a proof-of-concept to demonstrate how the secondary/spare region
+  in the nether might be put to use by someone.
+
+
+  Copyright (C) 2021 Treer
+
+  Permission to use, copy, modify, and/or distribute this software for
+  any purpose with or without fee is hereby granted, provided that the
+  above copyright notice and this permission notice appear in all copies.
+
+  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+  WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+  WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR
+  BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES
+  OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
+  WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+  ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+  SOFTWARE.
+
+]]--
+
+
+local debugf = nether.debug
+local mapgen = nether.mapgen
+
+
+-- Content ids
+
+local c_air              = minetest.get_content_id("air")
+local c_crystal          = minetest.get_content_id("nether:geodelite") -- geodelite has a faint glow
+local c_netherrack       = minetest.get_content_id("nether:rack")
+local c_glowstone        = minetest.get_content_id("nether:glowstone")
+
+-- Math funcs
+local math_max, math_min, math_abs, math_floor, math_pi = math.max, math.min, math.abs, math.floor, math.pi -- avoid needing table lookups each time a common math function is invoked
+
+
+-- Create a tiling space of close-packed spheres, using Hexagonal close packing
+-- of spheres with radius 0.5.
+-- With a layer of spheres on a flat surface, if the pack-z distance is 1 due to 0.5
+-- radius then the pack-x distance will be the height of an equilateral triangle: sqrt(3) / 2,
+-- and the pack-y distance between each layer will be sqrt(6) / 3,
+-- The tessellating space will be a rectangular box of 2*pack-x by 1*pack-z by 3*pack-y
+
+local xPack = math.sqrt(3)/2      -- 0.866, height of an equalateral triangle
+local xPack2 = xPack * 2          -- 1.732
+local yPack = math.sqrt(6) / 3    -- 0.816, y height of each layer
+local yPack2 = yPack * 2
+local yPack3 = yPack * 3
+local layer2offsetx = xPack / 3   -- 0.289, height to center of equalateral triangle
+local layer3offsetx = xPack2 / 3  -- 0.577
+local structureSize = 50 -- magic numbers may need retuning if this changes too much
+
+local layer1 = {
+    {0,      0,  0},
+    {0,      0,  1},
+    {xPack,  0, -0.5},
+    {xPack,  0,  0.5},
+    {xPack,  0,  1.5},
+    {xPack2, 0,  0},
+    {xPack2, 0,  1},
+}
+local layer2 = {
+    {layer2offsetx - xPack,  yPack,  0},
+    {layer2offsetx - xPack,  yPack,  1},
+    {layer2offsetx,          yPack, -0.5},
+    {layer2offsetx,          yPack,  0.5},
+    {layer2offsetx,          yPack,  1.5},
+    {layer2offsetx + xPack,  yPack,  0},
+    {layer2offsetx + xPack,  yPack,  1},
+    {layer2offsetx + xPack2, yPack, -0.5},
+    {layer2offsetx + xPack2, yPack,  0.5},
+    {layer2offsetx + xPack2, yPack,  1.5},
+}
+local layer3 = {
+    {layer3offsetx - xPack,  yPack2, -0.5},
+    {layer3offsetx - xPack,  yPack2,  0.5},
+    {layer3offsetx - xPack,  yPack2,  1.5},
+    {layer3offsetx,          yPack2,  0},
+    {layer3offsetx,          yPack2,  1},
+    {layer3offsetx + xPack,  yPack2, -0.5},
+    {layer3offsetx + xPack,  yPack2,  0.5},
+    {layer3offsetx + xPack,  yPack2,  1.5},
+    {layer3offsetx + xPack2, yPack2,  0},
+    {layer3offsetx + xPack2, yPack2,  1},
+}
+local layer4 = {
+    {0,      yPack3,  0},
+    {0,      yPack3,  1},
+    {xPack,  yPack3, -0.5},
+    {xPack,  yPack3,  0.5},
+    {xPack,  yPack3,  1.5},
+    {xPack2, yPack3,  0},
+    {xPack2, yPack3,  1},
+}
+local layers = {
+    {y = layer1[1][2], points = layer1}, -- layer1[1][2] is the y value of the first point in layer1, and all spheres in a layer have the same y
+    {y = layer2[1][2], points = layer2},
+    {y = layer3[1][2], points = layer3},
+    {y = layer4[1][2], points = layer4},
+}
+
+
+-- Geode mapgen functions (AKA proof of secondary/spare region concept)
+
+
+-- fast for small lists
+function insertionSort(array)
+    local i
+    for i = 2, #array do
+        local key = array[i]
+        local j = i - 1
+        while j > 0 and array[j] > key do
+            array[j + 1] = array[j]
+            j = j - 1
+        end
+        array[j + 1] = key
+    end
+    return array
+end
+
+
+local distSquaredList = {}
+local adj_x = 0
+local adj_y = 0
+local adj_z = 0
+local lasty, lastz
+local warpx, warpz
+
+
+-- It's quite a lot to calculate for each air node, but its not terribly slow and
+-- it'll be pretty darn rare for chunks in the secondary region to ever get emerged.
+mapgen.getGeodeInteriorNodeId = function(x, y, z)
+
+	if z ~= lastz then
+		lastz = z
+		-- Calculate structure warping
+		-- To avoid calculating this for each node there's no warping as you look along the x axis :(
+		adj_y = math.sin(math_pi / 222 * y) * 30
+
+		if y ~= lasty then
+			lasty = y
+			warpx = math.sin(math_pi / 100 * y) * 10
+			warpz = math.sin(math_pi /  43 * y) * 15
+		end
+		local twistRadians = math_pi / 73 * y
+		local sinTwist, cosTwist = math.sin(twistRadians), math.cos(twistRadians)
+		adj_x = cosTwist * warpx - sinTwist * warpz
+		adj_z = sinTwist * warpx + cosTwist * warpz
+	end
+
+	-- convert x, y, z into a position in the tessellating space
+	local cell_x = (((x + adj_x) / xPack2 + 0.5) % structureSize) / structureSize * xPack2
+	local cell_y = (((y + adj_y) / yPack3 + 0.5) % structureSize) / structureSize * yPack3
+	local cell_z = (((z + adj_z) + 0.5) % structureSize) / structureSize -- zPack = 1, so can be omitted
+
+	local iOut = 1
+	local i, j
+	local canSkip = false
+
+	for i = 1, #layers do
+
+		local layer = layers[i]
+		local dy = cell_y - layer.y
+
+		if dy > -0.71 and dy < 0.71 then -- optimization - don't include points to far away to make a difference. (0.71 comes from sin(45°))
+			local points = layer.points
+
+			for j = 1, #points do
+
+				local point = points[j]
+				local dx = cell_x - point[1]
+				local dz = cell_z - point[3]
+				local distSquared = dx*dx + dy*dy + dz*dz
+
+				if distSquared < 0.25 then
+					-- optimization - point is inside a sphere, so cannot be a wall edge. (0.25 comes from radius of 0.5 squared)
+					return c_air
+				end
+
+				distSquaredList[iOut] = distSquared
+				iOut = iOut + 1
+			end
+		end
+	end
+
+	-- clear the rest of the array instead of creating a new one to hopefully reduce luajit mem leaks.
+	while distSquaredList[iOut] ~= nil do
+		rawset(distSquaredList, iOut, nil)
+		iOut = iOut + 1
+	end
+
+	insertionSort(distSquaredList)
+
+	local d3_1 = distSquaredList[3] - distSquaredList[1]
+	local d3_2 = distSquaredList[3] - distSquaredList[2]
+	--local d4_1 = distSquaredList[4] - distSquaredList[1]
+	--local d4_3 = distSquaredList[4] - distSquaredList[3]
+
+	-- Some shape formulas (tuned for a structureSize of 50)
+	--   (d3_1 < 0.05) gives connective lines
+	--   (d3_1 < 0.05 or d3_2 < .02) give fancy elven bridges - prob doesn't need the d3_1 part
+	--  ((d3_1 < 0.05 or d3_2 < .02) and distSquaredList[1] > .3) tapers the fancy connections in the middle
+	--   (d4_3 < 0.03 and d3_2 < 0.03) produces caltrops at intersections
+	--   (d4_1 < 0.1) produces spherish balls at intersections
+	-- The idea is voronoi based - edges in a voronoi diagram are where each nearby point is at equal distance.
+	-- In this case we use squared distances to avoid calculating square roots.
+
+	if (d3_1 < 0.05 or d3_2 < .02) and distSquaredList[1] > .3 then
+		return c_crystal
+	elseif (distSquaredList[4] - distSquaredList[1]) < 0.08 then
+		return c_glowstone
+	else
+		return c_air
+	end
+end
\ No newline at end of file
diff --git a/mod.conf b/mod.conf
index 76467cb..50426d2 100644
--- a/mod.conf
+++ b/mod.conf
@@ -1,4 +1,4 @@
 name = nether
 description = Adds a deep underground realm with different mapgen that you can reach with obsidian portals.
 depends = stairs, default
-optional_depends = moreblocks, mesecons, loot, dungeon_loot, doc_basics, fire, climate_api, ethereal, walls
+optional_depends = moreblocks, mesecons, loot, dungeon_loot, doc_basics, fire, climate_api, ethereal, xpanes, walls
diff --git a/nodes.lua b/nodes.lua
index 9aa0d9d..52503f2 100644
--- a/nodes.lua
+++ b/nodes.lua
@@ -180,6 +180,63 @@ minetest.register_node("nether:rack", {
 	sounds = default.node_sound_stone_defaults(),
 })
 
+-- Geode crystals can only be introduced by the biomes-based mapgen, since it requires the
+-- MT 5.0 world-align texture features.
+minetest.register_node("nether:geode", {
+	description = S("Nether Beryl"),
+	_doc_items_longdesc = S("Nether geode crystal, found lining the interior walls of Nether geodes"),
+	tiles = {{
+		name        = "nether_geode.png",
+		align_style = "world",
+		scale       = 4
+	}},
+	is_ground_content = true,
+	groups = {cracky = 3, oddly_breakable_by_hand = 3, nether_crystal = 1},
+	sounds = default.node_sound_glass_defaults(),
+})
+
+-- Nether Berylite is a Beryl that can seen in the dark, used to light up the internal structure
+-- of the geode, so to avoid player confusion we'll just have it drop plain Beryl, and have only
+-- plain Beryl in the creative inventory.
+minetest.register_node("nether:geodelite", {
+	description = S("Nether Berylite"),
+	_doc_items_longdesc = S("Nether geode crystal. A crystalline structure with faint glow found inside large Nether geodes"),
+	tiles = {{
+		name        = "nether_geode.png",
+		align_style = "world",
+		scale       = 4
+	}},
+	light_source = 2,
+	drop = "nether:geode",
+	is_ground_content = true,
+	groups = {cracky = 3, oddly_breakable_by_hand = 3, nether_crystal = 1, not_in_creative_inventory = 1},
+	sounds = default.node_sound_glass_defaults(),
+})
+
+if minetest.get_modpath("xpanes") and minetest.global_exists("xpanes") and xpanes.register_pane ~= nil then
+	xpanes.register_pane("nether_crystal_pane", {
+		description = S("Nether Crystal Pane"),
+		textures = {
+			{
+				name        = "nether_geode_glass.png",
+				align_style = "world",
+				scale       = 2
+			},
+			"",
+			"xpanes_edge_obsidian.png"
+		},
+		inventory_image = "([combine:32x32:-8,-8=nether_geode_glass.png:24,-8=nether_geode_glass.png:-8,24=nether_geode_glass.png:24,24=nether_geode_glass.png)^[resize:16x16^[multiply:#922^default_obsidian_glass.png",
+		wield_image     = "([combine:32x32:-8,-8=nether_geode_glass.png:24,-8=nether_geode_glass.png:-8,24=nether_geode_glass.png:24,24=nether_geode_glass.png)^[resize:16x16^[multiply:#922^default_obsidian_glass.png",		use_texture_alpha = true,
+		sounds = default.node_sound_glass_defaults(),
+		groups = {snappy=2, cracky=3, oddly_breakable_by_hand=3},
+		recipe = {
+			{"group:nether_crystal", "group:nether_crystal", "group:nether_crystal"},
+			{"group:nether_crystal", "group:nether_crystal", "group:nether_crystal"}
+		}
+	})
+end
+
+
 -- Deep Netherrack, found in the mantle / central magma layers
 minetest.register_node("nether:rack_deep", {
 	description = S("Deep Netherrack"),
diff --git a/textures/nether_geode.png b/textures/nether_geode.png
new file mode 100644
index 0000000..6835c86
Binary files /dev/null and b/textures/nether_geode.png differ
diff --git a/textures/nether_geode_glass.png b/textures/nether_geode_glass.png
new file mode 100644
index 0000000..4921c7b
Binary files /dev/null and b/textures/nether_geode_glass.png differ