Table 4 Type classifications of volcanic ashes from the 2018–2019 eruption at Kuchinoerabujima Volcano
Type | Type-1 | Type-2 | Type-3 | ||||
|---|---|---|---|---|---|---|---|
Non-altered | Partially altered | Intensely altered | |||||
Sub-type | Type 3–1 | Type 3–2 | Type 3–3 | Type 3–4 | Type 3–5 | ||
Name of particle | Silica | Sulfate | Sulfide | Sulfur-bearing | Others | ||
Optical discription | -Glassy luster, translucent gray-color to transparent dark-color particles Angular to sub-angular shape | Translucent gray- to white-color particles Angular to sub-angular shapes | White-, yellowish brown-, or dark-colored particles Angular to rounded shapes | ||||
X-ray map (intense elements) | Si, Al, K | Si, Al, K | Si | S, Ca | S, Fe | S | Al, K, Ca |
Minerals contained | … | … | Silica mineral(s) | Sulfate mineral(s) | Sulfide mineral | Sulfur-bearing minerals | zeolite group minerals? clay minerals? |
… | … | Qz, Cri, Tri | Gyp, Anh, Alu | Pyr | Gyp, Anh | ||
Textural description | -no traces of alteration | Groundmass: consisting of fine aggregate of anhedral silica minerals, unclear crystal boundary of microlite and tabular to irregular voids Original volcanic rock textures are replaced to silica minerals and minor hydrothermal clay mineral(s) | … | [Type 3-2C] An aggregate of coarse euhedral sulfate crystals [Type 3-2F] Euhedral sulfate crystals included in the aggregate of fine silica and clay minerals | Mainly pyrite and sulfate minerals with minor silica and clay minerals | Minor but commonly contain gypsum and/or anhydrite crystals | … |