Feldspathoid in the context of Pluton

Analcime (/əˈnælsiːm, -saɪm/; from Ancient Greek ἀνάλκιμος (análkimos) 'not strong') or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is NaAlSi₂O₆ · H₂O. Minor amounts of potassium and calcium substitute for sodium. A silver-bearing synthetic variety also exists (Ag-analcite).

Analcime is usually classified as a zeolite mineral, but structurally and chemically it is more similar to the feldspathoids. Analcime is not classified as an isometric crystal, as although the crystal structure appears to be isometric, it is usually off only by a fraction of an angle. However, there are truly isometric samples of the mineral, which makes its classification even more difficult. Due to the differences between the samples being too slight, there's no merit from having multiple species names, so as a result analcime is a common example for minerals occurring in multiple crystal systems and space groups.

In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and compositions, illustrated by examples like the Palisades Sill of New York and New Jersey; the Henry Mountains of Utah; the Bushveld Igneous Complex of South Africa; Shiprock in New Mexico; the Ardnamurchan intrusion in Scotland; and the Sierra Nevada Batholith of California.

Because the solid country rock into which magma intrudes is an excellent insulator, cooling of the magma is extremely slow, and intrusive igneous rock is coarse-grained (phaneritic). Intrusive igneous rocks are classified separately from extrusive igneous rocks, generally on the basis of their mineral content. The relative amounts of quartz, alkali feldspar, plagioclase, and feldspathoid is particularly important in classifying intrusive igneous rocks.

A QAPF diagram is a doubled-triangle plot diagram used to classify igneous rocks based on their mineralogy. The acronym QAPF stands for "quartz, alkali feldspar, plagioclase, feldspathoid (foid)", which are the four mineral groups used for classification in a QAPF diagram. The percentages (ratios) of the Q, A, P and F groups are normalized, i.e., recalculated so that their sum is 100%.

Nepheline (from Ancient Greek νεφέλη (nephélē) 'cloud'), also called nephelite, is a rock-forming mineral in the feldspathoid group – a silica-undersaturated aluminosilicate (Na₃KAl₄Si₄O₁₆) that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. It is used in glass and ceramic manufacturing and other industries, and has been investigated as an ore of aluminium.

A granitoid is a broad term referring to a diverse group of coarse-grained igneous rocks that are widely distributed across the globe, covering a significant portion of the Earth's exposed surface and constituting a large part of the continental crust. These rocks are primarily composed of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz-poor monzonites to quartz-rich quartzolites. As only two of the three defining mineral groups (quartz, plagioclase, and alkali feldspar) need to be present for the rock to be called a granitoid, foid-bearing rocks, which predominantly contain feldspars but no quartz, are also granitoids.

Lazurite, old name Azure spar is a tectosilicate mineral with sulfate, sulfur and chloride with formula (Na,Ca)₈[(S,Cl,SO₄,OH)₂|(Al₆Si₆O₂₄)]. It is a feldspathoid and a member of the sodalite group. Lazurite crystallizes in the isometric system although well‐formed crystals are rare. It is usually massive and forms the bulk of the gemstone lapis lazuli.

Leucite (from the Greek word leukos meaning white) is a rock-forming mineral of the feldspathoid group, silica-undersaturated and composed of potassium and aluminium tectosilicate KAlSi₂O₆. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in 1821, they are not optically isotropic, and are therefore pseudo-cubic. Goniometric measurements made by Gerhard vom Rath in 1873 led him to refer the crystals to the tetragonal system. Optical investigations have since proved the crystals to be still more complex in character, and to consist of several orthorhombic or monoclinic individuals, which are optically biaxial and repeatedly twinned, giving rise to twin-lamellae and to striations on the faces. When the crystals are raised to a temperature of about 500 °C they become optically isotropic and the twin-lamellae and striations disappear, although they reappear when the crystals are cooled again. This pseudo-cubic character of leucite is very similar to that of the mineral boracite. Leucite is commonly found in igneous rocks, especially at Mt. Vesuvius

The crystals are white or ash-grey in colour, hence the name suggested by A. G. Werner in 1701, from λευκος, '(matt) white'. They are transparent and glassy when fresh, albeit with a noticeably subdued 'subvitreous' lustre due to the low refractive index, but readily alter to become waxy/greasy and then dull and opaque; they are brittle and break with a conchoidal fracture. The Mohs hardness is 5.5, and the specific gravity 2.47. Inclusions of other minerals, arranged in concentric zones, are frequently present in the crystals. On account of the color and form of the crystals the mineral was early known as 'white garnet'. French authors in older literature may employ René Just Haüy's name amphigène, but 'leucite' is the only name for this mineral species that is recognised as official by the International Mineralogical Association.

Latite is an igneous, volcanic rock, with aphanitic-aphyric to aphyric-porphyritic texture. It is the volcanic equivalent of monzonite. Its mineral assemblage is usually alkali feldspar and plagioclase in approximately equal amounts. Quartz is less than five percent and is absent in a feldspathoid-bearing latite, and olivine is absent in a quartz-bearing latite. When quartz content is greater than five percent the rock is classified as quartz latite. Biotite, hornblende, pyroxene and scarce olivine or quartz are common accessory minerals. Feldspathoid-bearing latite is sometimes referred to as tristanite.

Rhomb porphyries are an unusual variety with gray-white porphyritic, rhomb-shaped phenocrysts embedded in a very fine grained red-brown matrix. The composition of rhomb porphyry places it in the trachyte - latite classification of the QAPF diagram.

Hauyne or haüyne, also called hauynite or haüynite (/ɑːˈwiːnaɪt/ ah-WEE-nyte), old name Azure spar, is a rare tectosilicate sulfate mineral with endmember formula Na₃Ca(Si₃Al₃)O₁₂(SO₄). As much as 5 wt % K₂O may be present, and also H₂O and Cl. It is a feldspathoid and a member of the sodalite group. Hauyne was first described in 1807 from samples discovered in Vesuvian lavas in Monte Somma, Italy, and was named in 1807 by Brunn-Neergard for the French crystallographer René Just Haüy (1743–1822). It is sometimes used as a gemstone.

Nosean, also known as noselite, is a mineral of the feldspathoid group with formula: Na₈(Al₆Si₆O₂₄)(SO₄)·H₂O. It forms isometric crystals of variable color: white, grey, blue, green, to brown. It has a Mohs hardness of 5.5 to 6 and a specific gravity of 2.3 to 2.4. It is fluorescent. It is found in low-silica igneous rocks. There is a solid solution between nosean and hauyne, which contains calcium.

It was first described in 1815 from the Rhineland in Germany and named after the German mineralogist K. W. Nose (1753–1835). The mineral is rare but widespread, found in such diverse localities as ocean islands (e.g., Tahiti) and the La Sal Range in Utah.

Tugtupite is a beryllium aluminium tectosilicate. It also contains sodium and chlorine and has the formula Na₄AlBeSi₄O₁₂Cl. Tugtupite is a member of the silica-deficient feldspathoid mineral group. It occurs in high alkali intrusive igneous rocks.

Tugtupite is tenebrescent, sharing much of its crystal structure with sodalite, and the two minerals are occasionally found together in the same sample.