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Table T1. Glossary of metamorphic petrology terms.

Term Definition
Apparent fibers Cross sections of serpentine plates that look fibrous in thin section.
Asbestiform Crystals (chrysotile, tremolite) are thin hairlike fibers that are mechanically separable.
Background alteration Alteration has pervasively affected the entire rock and is not primarily bound to veins or foliation planes.
Banded vein Vein with rhythmic layering parallel to the vein walls.
Bastite Serpentine texture after chain and layer silicates preserving important features of the protolith (e.g., plastic deformation) and preserpentine alteration assemblages.
Brucite Brucite was tentatively identified by anomalous cream-brown interference colors, by yellow color in plane-polarized light (if weathered), and by shape (more bladed or prismatic than serpentine).
Chrysotile White asbestiform serpentine, usually in veins with magnetite; most common in paragranular veins.
Composite vein Compositionally zoned vein containing different mineral assemblages that may or may not represent different generations.
Cross-fiber vein Asbestiform or pseudofibrous vein in which the fibers (or apparent fibers) are oriented perpendicular to the vein walls.
Fault vein Vein material within a fault or cataclastic zone interpreted to be genetically related to the fault movement but lacking clear pull-apart geometries.
Fibrous Single crystals resembling organic fibers or crystalline aggregates that look like they are composed of fibers. If fibers are mechanically separable (e.g., by probing the sample with a needle), they are asbestiform. If they are not separable, they are pseudofibrous. If the fibers have the normal strength and brittleness of the mineral, they are acicular.
Hourglass texture Similar to mesh texture, but a distinction between mesh rim and mesh center is not possible. This texture is related to fractures in the mineral grains of the protolith and is, hence, not strictly a pseudomorphic texture.
Interlocking texture More or less equant serpentine grains and/or serrate serpentine veins replace pseudomorphic serpentine.
Interpenetrating texture Elongate, interpenetrating blades of γ-serpentine replace pseudomorphic serpentine.
Intravenous vein Veins that are entirely or almost entirely restricted to the interior of previous veins, without penetrating the matrix. Generally referred to as composite if parallel to the previous veins.
Massive vein Veins that are homogeneous and completely filled, with no identifiable internal texture.
Mesh texture Pseudomorphic texture resembling a fisherman’s net. The mesh rim represents the cord of the net and the mesh centers represent the empty areas between the cords of the net. The outer edge of a mesh cell coincides either with the edge of a mineral grain or with a fracture within the mineral grain of the protolith.
Nonpseudomorphic texture Does not preserve the texture of the protolith. Can only be recognized under cross-polarized light. Includes interpenetrating and interlocking textures.
Patch Polycrystalline domain, more or less isolated and surrounded by host rock, that is compositionally distinct from the host rock. Patches can be secondary features (i.e., as a consequence of patchy alteration) or primary igneous features where the differences may have been enhanced by alteration.
Picrolite Vein-filling serpentine that is white, cream, or pale yellow to apple green in color and may be either massive or pseudofibrous in habit. Picrolite can be lizardite, chrysotile, or antigorite.
Polycrystalline vein Vein clearly containing separate mineral grains. Can be mono- or polymineralic.
Pull-apart vein Veins developed in extensional jogs on faults. Can be used to identify the direction of fault slip.
Pseudofibrous Crystals or crystalline aggregates that have fibrous appearance but are not composed of separable fibers.
Pseudomorphic texture Preserves the texture of the protolith. Includes mesh and hourglass textures. Can be recognized in plane-polarized light.
Ribbon texture Special form of transitional texture. Mesh rims extend over several grains of the protolith, creating a set of irregular bands.
Rodingite A calcium metasomatized rock in which the primary igneous composition and texture have been destroyed to an extent that the nature of the protolith is uncertain. If the nature of the protolith can be discerned but calcium metasomatism is obvious, the rock is described as rodingitized.
Selvages Wallrock along a vein that is completely altered to secondary minerals and has a sharp contact with the host rock.
Slip-fiber vein Asbestiform or pseudofibrous vein in which the fibers (or apparent fibers) are oriented more or less parallel to the vein walls.
Transgranular vein Vein or vein network at any angle to the foliation planes that crosscut porphyroclasts and/or other large crystals.
Transitional texture Preserves some of the texture of the protolith. May appear pseudomorphic in plane-polarized light but without mesh or hourglass texture in cross-polarized light. Includes mesh textures with isotropic mesh centers and ribbon textures.
Type 1 hourglass texture Extinction sweeps continuously across mesh center.
Type 2 hourglass texture Recrystallization of serpentine has produced a mottled extinction pattern.
Vein halos Zones (1 mm–1 cm wide) along a vein in which the rock is more intensely altered, or altered in a different style, than the host rock. A halo can have a sharp or diffuse contact with the host rock.
Vuggy vein Incompletely filled vein.
α-Serpentine Length-fast fibers.
γ-Serpentine Length-slow fibers.

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