Fundamental Minerals

Sialic Minerals

• Feldspar
Feldspar
Sanidine
Plagioclase

• Feldspathoid
Feldspathoids
Haüyne
Kalsilite
Leucite
Nepheline


• Quartz

Femic Minerals

• Amphiboles
• Aenigmatite
• Biotite
• Sagenitic biotite
• Melilite
• Olivine
• Pyroxene
Structure
Clinopyroxene
Orthopyroxene

Accessory Minerals

• Andradite
• Apatite
• Cordierite
• Chromite
• Magnetite
• Ilmenite
• Titanite

Very Rare Minerals

• Gregorite
• Nyerereite
• Priderite

Secondary Minerals

• Calcite
• Chlorite
• Hematite
• Epidote
• Orpiment
• Phillipsite
• Pinite

Texture

• Amygdales
• Embayed
• Eutaxitic
• Felsic
• Glomerophyric
• Hyalopilitic
• Hypocrystalline
• Holohyaline
• Intergranular
• Intersertal
• Magmatic flow
• Opacitic rim
• Ophitic
• Poikilitic
• Pilotassitic
• Porphyritic
• Sieve
• Skeletal
• Spinifex
• Trachytic
• Vitrophyric
• Zoning
• Xenocryst
• Xenolith

Alteration Products

• Bowlingite
• Iddingsite
• Pseudomorph
• Saussurite
• Sericite
• Uralite

Glass and related Texture

• Volcanic glass
• Fiamme
• Perlite
• Palagonite
• Spherulites
• Shards

Volcanic Rocks

• Aillikite
• Alnöite
• Andesite
• Ankaramite
• Basalt
• Benmoreite
• Bergalite
• Comendite
• Coppaelite
• Dacite
• Dacite (devitrified)
• Garnet dacite
• Foidite
• Foidite (nepheline)
• Haüynophyre
• Hyaloclastite
• Horneblende Andesite
• Ignimbrite
• Ignimbrite (pantelleritic)
• Kaiserstuhl
Kaiserstuhl
Bergalite
Carbonatitic lapillistone
Diatreme breccia
Limburgite
Olivine nephelinite
Tephrite
Sövite
Wollastonite phonolite

• Kersantite
• Kimberlites
Kimberlites
Varty lake (Canada)
Sturgeon lake (Canada)
Monastery (S.Africa)
Udachnaya (Russia)
• Komatiites
Komatiites
Alexo (Canada)
Belingwe (Zimbawe)

• Lamprophyres
Lamprophyres
Aillikite
Alnöite
Bergalite
Kersantite
Monchiquite
Sannaite
Spessartite
Vosegite

• Lapillistone
• Latite
• Leucitite
• Limburgite
• Madupite (lamproite)
• Mafurite
• Monchiquite
• Natrocarbonatite
• Obsidian
• Oldoinyo Lengai
Ol Doinyo Lengai
Natrocarbonatite lava

• Peperine
• Pyroclastic flow
• Pitchstone
• Pillow lava
• Pumice
• Rhyolite
• Sannaite
• Scoria (basaltic)
• Scoria (phonolitic)
• Spessartite
• Tephrite
• Tephritic leucitite
• Tephritic phonolite
• Trachybasalt
• Trachyte
• Trachyte (foid-bearing)
• Venanzite
• Vitrophyre
• Vosegite

Ignimbrite

The term "ignimbrite" (from the Latin igni- "fire" and imbri- "rain") was coined by the New Zealand geologist Peter Marshall in 1935. This term was originally used only to refer to welded tuffs. These are pyroclastic rocks that were so hot right after the deposition from the pyroclastic cloud that individual clasts adhered to each other. However, this restriction no longer applies. The term "ignimbrite" includes all pyroclastic flow deposits, no matter whether they are welded or not.

An ignimbrite is a welded pyroclastic rock that contains abundant flattened juvenile clasts often originally pumice. The flattened clasts within ignimbrites are termed fiamme and range from lapilli-sized (>2 mm) to block-sized (>64 mm). The layered texture produced by fiamme is termed a eutaxitic texture. The groundmass of ignimbrites is usually dominated flattened vitric shards, but can contain lithic and crystal fragments. The fine-grained groundmass of many ignimbrites has a reddish colour due to high temperature oxidation of iron, in particular in the upper parts of a pyroclastic flow deposit. Less welded flows tend to be white or grey, whilst intensely welded flows are often dark grey to black. Recrystallisation and alteration of glass within ignimbrite is common, in particular in ancient examples.

Ignimbrites form due to emplacement of high temperature pyroclastic flows that compact under their own weight. Exsolution of volatiles from pyroclasts after emplacement can cause alteration of the surrounding groundmass and generate vesicles. Rheomorphic flow of ignimbrites can occur after emplacement resulting in deformation of layering, clasts and vesicles. In thick ignimbrites columnar jointing may occur due to contraction during slow cooling.

The mineralogy of an ignimbrite is controlled primarily by the chemistry of the source magma. The typical range of phenocrysts in ignimbrites are biotite, quartz, sanidine or other alkali feldspar, occasionally hornblende, rarely pyroxene and in the case of phonolite tuffs, the feldspathoid minerals such as nepheline and leucite. Commonly in most felsic ignimbrites the quartz polymorphs cristobalite and tridymite are usually found within the welded tuffs and breccias. In the majority of cases, it appears that these high-temperature polymorphs of quartz occurred post-eruption as part of an autogenic post-eruptive alteration in some metastable form. Thus although tridymite and cristobalite are common minerals in ignimbrites, they may not be primary magmatic minerals.

Ignimbrite sample from the Southern coast of Gran Canaria. Note the strongly flattened pumice fragments (fiamme). From Sand Atlas.

Ignimbrite sample from the Western part of Gran Canaria. From Sand Atlas.

Ignimbrite sample from the NE coast of Gran Canaria. From Sand Atlas.

Bibliography

• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Le Maitre, R. W., Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., Bateman, P., & Lameyre, J. (2002). Igneous rocks. A classification and glossary of terms, 2. Cambridge University Press.
• Middlemost, E. A. (1986). Magmas and magmatic rocks: an introduction to igneous petrology.
• Shelley, D. (1993). Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press.

Photo

Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)
Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. XPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. XPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)
Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. XPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. XPL image, 2x (Field of view = 7mm)
Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)
Dacitic ignimbrite with fragmented crystals (Feldspar Biotite and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar Biotite and Hornblende). Equador. XPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar Biotite and Hornblende). Equador. PPL image, 10x (Field of view = 2mm)
Dacitic ignimbrite with fragmented crystals (Feldspar Biotite and Hornblende). Equador. XPL image, 10x (Field of view = 2mm)	Dacitic ignimbrite with fragmented crystals (Feldspar Biotite and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar Biotite and Hornblende). Equador. XPL image, 2x (Field of view = 7mm)
Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)	Dacitic ignimbrite with fragmented crystals (Feldspar and Hornblende). Equador. PPL image, 2x (Field of view = 7mm)	Ignimbrite (Peperine) with fragmented crystals (Feldspar and Orhopyroxene). Vulsini volcano (Italy). PPL image, 10x (Field of view = 2mm)
Ignimbrite (Peperine) with fragmented crystals (Feldspar and Orhopyroxene). Vulsini volcano (Italy). XPL image, 10x (Field of view = 2mm)	Ignimbrite (Peperine) with fragmented crystals (Feldspar Biotite and Clinopyroxene). Vulsini volcano (Italy). XPL image, 2x (Field of view = 7mm)	Ignimbrite (Peperine) with fragmented crystals (Feldspar Biotite and Clinopyroxene). Vulsini volcano (Italy). PPL image, 2x (Field of view = 7mm)
Flow structures in a Ignimbrite with green Hornblende, Milos (Greece). PPL image, 2x (Field of view = 7mm)	Flow structures in a Ignimbrite with green Hornblende, Milos (Greece). PPL image, 2x (Field of view = 7mm)	Flow structures in a Ignimbrite with green Hornblende, Milos (Greece). PPL image, 2x (Field of view = 7mm)
Flow structures in a Ignimbrite with green Hornblende, Milos (Greece). PPL image, 2x (Field of view = 7mm)	Flow structures in a Ignimbrite, Milos (Greece). PPL image, 10x (Field of view = 2mm)	Flow structures and Spherulite on a plegioclase in a Ignimbrite, Milos (Greece). PPL image, 10x (Field of view = 2mm)
Flow structures in a Ignimbrite, Milos (Greece). PPL image, 10x (Field of view = 2mm)	Flow structures and Spherulite on a plegioclase in a Ignimbrite, Milos (Greece). PPL image, 10x (Field of view = 2mm)	Flow structures in a Ignimbrite, Milos (Greece). PPL image, 10x (Field of view = 2mm)
Feldspar, Biotite and pyroxene embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)	Feldspar, Biotite and pyroxene embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 2x (Field of view = 7mm)	Feldspar and Biotite embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)
Feldspar crystal embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)	Feldspar crystal embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)	Feldspar crystal embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)
Feldspar crystal embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)	Feldspar and biotite crystals embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)	Feldspar and biotite crystals embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)
Feldspar and biotite crystals embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)	Feldspar crystals embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)	Feldspar embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)
Feldspar and biotite crystals embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)	Feldspar and biotite crystals embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)	Feldspar and biotite crystals embedded in a groundmass with fluidal textures, Lemnos (Greece). PPL image, 10x (Field of view = 2mm)
Feldspar embedded in a groundmass with fluidal textures. PPL image, 10x (Field of view = 2mm)	Feldspar crystals embedded in a groundmass with fluidal textures. PPL image, 10x (Field of view = 2mm)	Feldspar crystals embedded in a groundmass with fluidal textures. PPL image, 10x (Field of view = 2mm)
Feldspar crystals embedded in a groundmass with fluidal textures. PPL image, 10x (Field of view = 2mm)	Feldspar crystals embedded in a groundmass with fluidal textures. PPL image, 10x (Field of view = 2mm)	Feldspar crystals embedded in a groundmass with fluidal textures. PPL image, 10x (Field of view = 2mm)

Xenoliths

Xenolith embedded in a groundmass with fluidal textures. PPL image, 10x (Field of view = 2mm)	Xenoliths embedded in a groundmass with fluidal textures. PPL image, 10x (Field of view = 2mm)	Xenolith embedded in a groundmass with fluidal textures. PPL image, 10x (Field of view = 2mm)
Xenolith in a ignimbrite. PPL image, 10x (Field of view = 2mm)	Xenolith in a ignimbrite. XPL image, 10x (Field of view = 2mm)	Xenolith in a ignimbrite. PPL image, 10x (Field of view = 2mm)
Xenolith in a ignimbrite. PPL image, 10x (Field of view = 2mm)	Xenolith in a ignimbrite. PPL image, 10x (Field of view = 2mm)	Xenolith in a ignimbrite. XPL image, 10x (Field of view = 2mm)
Xenoliths in a ignimbrite. PPL image, 10x (Field of view = 2mm)	Xenoliths in a ignimbrite. PPL image, 10x (Field of view = 2mm)	Xenolith in a ignimbrite. XPL image, 10x (Field of view = 2mm)
Xenoliths in a ignimbrite. PPL image, 10x (Field of view = 2mm)	Xenoliths in a ignimbrite. PPL image, 10x (Field of view = 2mm)	Xenolith in a ignimbrite. XPL image, 10x (Field of view = 2mm)