(Java Minecraft 1.14) How to set the probability of nested entries in a loot table?

Ok, so after a bit of thinking time I got it. Here is the file:

{
  "type": "minecraft:block",
  "pools": [
    {
      "rolls": 1,
      "entries": [
        {
          "type": "minecraft:alternatives",
          "children": [
            {
              "type": "minecraft:item",
              "conditions": [
                {
                  "condition": "minecraft:match_tool",
                  "predicate": {
                    "enchantments": [
                      {
                        "enchantment": "minecraft:silk_touch",
                        "levels": {
                          "min": 1
                        }
                      }
                    ]
                  }
                }
              ],
              "name": "minecraft:nether_quartz_ore"
            },
            {
              "type": "minecraft:sequence",
              "children": [
                {
                  "type": "minecraft:item",
                  "functions": [
                    {
                      "function": "minecraft:apply_bonus",
                      "enchantment": "minecraft:fortune",
                      "formula": "minecraft:ore_drops"
                    },
                    {
                      "function": "minecraft:explosion_decay"
                    }
                  ],
                  "name": "minecraft:quartz"
                },
                {
                  "type": "minecraft:item",
                  "conditions": [
                    {
                      "condition": "random_chance",
                      "chance": 0.05
                    }
                  ],
                  "functions": [
                    {
                      "function": "set_name",
                      "name": {"text":"Dark Quartz","color":"dark_gray","italic":"false"}
                    },
                    {
                      "function": "set_nbt",
                      "tag": "{DarkQuartz:1b,CustomModelData:1}"
                    },
                    {
                      "function": "minecraft:explosion_decay"
                    }
                  ],
                  "name": "minecraft:quartz"
                }
              ]
            }
          ]
        }
      ]
    }
  ]
}

And now for an explanation: The loot table has one pool, with one roll, meaning that only one entry will be selected. That one entry is of the type "minecraft:alternatives", which means that the first entry with successful conditions out of several children sub-entries will be the one choosen. There are two children pools: one for silk touch picks and one for non silk touch picks. The first is of type "minecraft:item", meaning it just has an item, while the second is of the type "minecraft:sequence", meaning it has a few sub-entries of its own. If the first is chosen, one nether quartz ore is dropped and that's the end of things. If the first is NOT chosen, we go into the second entry, which as we said earlier is a "minecraft:sequence" type. This means that out of several children entries, items will be chosen from all entries in a row until an entry fails the conditions, at which point everything stops. We have two entries: the first with no conditions (meaning it will always give an item, provided we have not used a silk touch pick and are therefore in the "minecraft:sequence" entry) and the second with a "random_chance" condition (meaning it only gives an item when a randomly generated number between 0 and 1 is below the "chance" value,in this case 0.05). Testing shows it works: mining 20 nether quartz ores with a normal pick, I get 20 nether quartz and 1 dark quartz. With a silk touch pick I get 20 nether quartz ore, and with a fortune III pick I get 39 nether quartz and 1 dark quartz.