"alum stone" meaning in English

{
  "forms": [
    {
      "form": "alum stones",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "alum stone (plural alum stones)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "extra": "alunite",
          "word": "alumstone"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Minerals",
          "orig": "en:Minerals",
          "parents": [
            "Matter",
            "Mineralogy",
            "Chemistry",
            "Nature",
            "Geology",
            "Sciences",
            "All topics",
            "Earth sciences",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Alternative form of alumstone (“alunite”)"
      ],
      "id": "en-alum_stone-en-noun-R24oLzun",
      "links": [
        [
          "mineralogy",
          "mineralogy"
        ],
        [
          "alumstone",
          "alumstone#English"
        ],
        [
          "alunite",
          "alunite"
        ]
      ],
      "raw_glosses": [
        "(mineralogy) Alternative form of alumstone (“alunite”)"
      ],
      "tags": [
        "alt-of",
        "alternative"
      ],
      "topics": [
        "chemistry",
        "geography",
        "geology",
        "mineralogy",
        "natural-sciences",
        "physical-sciences"
      ]
    }
  ],
  "word": "alum stone"
}

{
  "forms": [
    {
      "form": "alum stones",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "alum stone (plural alum stones)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "extra": "alunite",
          "word": "alumstone"
        }
      ],
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "en:Minerals"
      ],
      "glosses": [
        "Alternative form of alumstone (“alunite”)"
      ],
      "links": [
        [
          "mineralogy",
          "mineralogy"
        ],
        [
          "alumstone",
          "alumstone#English"
        ],
        [
          "alunite",
          "alunite"
        ]
      ],
      "raw_glosses": [
        "(mineralogy) Alternative form of alumstone (“alunite”)"
      ],
      "tags": [
        "alt-of",
        "alternative"
      ],
      "topics": [
        "chemistry",
        "geography",
        "geology",
        "mineralogy",
        "natural-sciences",
        "physical-sciences"
      ]
    }
  ],
  "word": "alum stone"
}