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Term
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Explanation
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Breccia (Br)
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Type of breccia
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Hydrothermal (Bh), magmatic (Bm), tectonic (Bc)
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Volume percent
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Percent clasts vs. bulk rock
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Size range
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Maximum–minimum average size
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Shape
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Angular, subangular, subrounded, rounded, etc.
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Composition
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Monomictic, polymictic
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Structure
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Internal crushing, veining, fracturing, etc.; preferred orientation
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Alteration
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Alteration halos in the clasts
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Sorting
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Well sorted, moderately sorted, poorly sorted
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Volume percent
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Percent matrix vs. bulk rock
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Grain size
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Coarse, medium, fine
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Composition
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Lithology and/or mineralogy compared with clasts
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Structure
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Veining, fracturing, preferred orientation, shearing
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Alteration
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Alteration in the matrix
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Volume percent
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Percent cement vs. bulk rock
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Composition
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Mineralogy
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Veins (V)
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Vein type
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Magmatic/late magmatic (Vm), hydrothermal (Vh)
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Orientation of vein
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Vertical, horizontal
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Depth of vein
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Interval in the core
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Morphology
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Planar (Pl), curved (Cv), irregular (Ir), sigmoidal (Sg), stepped (St), T-shaped (T), Y-shaped (Y), splayed (S)
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Vein array geometry
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Conjugate, network, en echelon, anastomosing, riedel
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Vein density (N/10 cm)
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No vein, slight, moderate, high, complete
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Fabric of the filling minerals
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Fibrous (Fb), vermicular (Vr), blocky (Bl)
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Vein mineralogy
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Carbonate, quartz, Fe oxide, celadonite, etc.
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Average width and length
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Measured in millimeters
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Joints (J)
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Orientation of joint
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Direction of joint
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Depth of joint
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Interval within the core
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Morphology
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Planar (Pl), curvilinear (Cv), anastomosing (An), T-shaped (T), Y-shaped (Y), splayed (Spl), stepped (St)
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Joint array
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Conjugate, network, en echelon
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Joint density
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Number of joints in an ligneous unit or per core/site
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Faults (F)
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Orientation of fault
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Direction of fault
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Depth of fault
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Interval within the core
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Magnitude of the apparent offset
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Measured offset (on the cut face of the core and side wall)
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Apparent sense of shear
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Dextral (dx), sinistral (sx), reversed (r), normal (n)
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Crosscutting relationships
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Relative timing from one feature to another
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Average thickness of fault zone
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Fault zone thickness measured in millimeters
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Occurrence of alteration halos
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Halos associated with fluid flow through the fault zone
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Occurrence and type of fault rocks
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Rocks formed by faulting (e.g., cataclasite)
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Other
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Composite vein
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Compositionally and texturally zoned vein containing different mineral assemblages that may or may not represent different generations.
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Fabric
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Relative orientation of parts of a rock mass. Preferred linear orientation of part of a rock is termed linear fabric, preferred planar orientation is termed planar fabric, and lack of a preferred orientation is referred to as random fabric.
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Fault
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Fractures with kinematic evidence for shear displacement across the discontinuity or with an associated cataclasite.
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Foliation
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Any repetitively occurring penetrative planar feature in a rock body.
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Joint
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Fractures in which the two sides show no differential displacement (relative to the naked eye or 10× hand lens) and have no filling material.
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Shear vein
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Obliquely opening veins with minor shear displacement, filled with slickenfibers or overlapping fibers.
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Texture
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Relative size, shape, and spatial interrelationship between grains and internal features of grains in a rock.
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Vein
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Extensional or oblique open fractures filled with epigenic minerals.
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