The hyphen (-) looks like a short dash, but the hyphen and the dash are very different: whereas the hyphen unites, the dash separates.

In general, the hyphen is used between a word and a prefix, suffix, or other word-element, to prevent ambiguity of meaning or awkward-looking combinations of letters.

Words frequently used in close association tend to become unified in form as they are in meaning, and ultimately to acquire a single accent. There are three stages in the development of compounds. At first the components of the compound expression are written separately; next they are united by a hyphen; finally, when the separate significance and accent of these components have been lost sight of, they are combined into one word. The hyphenated stage may thus be considered merely preparatory to the coalescence of the various members into one word. Many such compounds have now fully coalesced and are written as one word, as (e.g. footwall, landmass, off-shore, rockburst).

Although the modern trend is to use hyphens sparingly, they are notoriously troublesome; no two dictionaries or books on grammar or style consistently give the same advice. This section therefore outlines the rules to be followed in GSC publications.

Nouns

Hyphenate the following:

1. nouns of equal value (or when used as adjectives):
   
   
   basin-and-range
   salt-and-pepper sandstone
   silver-gold anomaly
   cusp-ripple
   strike-slip fault
   lead-zinc vein
   shale-arenite
   vein-dyke
   stoss-and-lee topography
   
   
   
   
2. nouns written as two words, when they have a modifier:
   
   
   dispersed mineral-matter
   but mineral matter
   
   fixed entropy-ratio
   but entropy ratio
   
   isolated point-bar
   but point bar
   
   red colour-filter
   but colour filter
   
   
   
   
3. noun-plus-adjective compounds
   
   
   ice-rich snow
   the snow is ice-rich
   lichen-free rock
   the rock was lichen-free
   

Do not hyphenate the following:

a compound noun that has become a single specialized word:

but if such a noun has a modifier that modifies only the first part, the compound is separated by a hyphen:

Adjectives

Hyphens should be used to clarify possible ambiguities, so hyphenate in these instances:

1. compound adjectives when they precede the noun they modify:
   
   
   coarse-grained granite
   ice-marginal channel
   large-scale feature
   Hawaiian-type eruption
   low-pressure conditions
   high-angle fault
   low-velocity zone
   high-energy environment
   Mid-Atlantic Ridge
   high-grade metamorphism
   shallow-marine environment
   ice-contact deposit
   small-scale map
   ice-flow direction
   thin-bedded limestone
   
   
   
   
2. combination colour terms placed before or after the noun:
   
   
   blue-green amphibole the amphibole is blue-green
   orange-red shear zone the shear zone is orange-red
   
   
   Compounds with the suffix -ish are hyphenated only when they precede the noun:
   
   
   bluish-green amphibole
   but the amphibole is bluish green
   
   
   Adjectives indicating a specific shade, such as light, pale, bright, dark are not hyphenated if they are placed before or after the noun:
   
   
   light grey gneiss
   the gneiss is light grey
   pale yellow zone
   the zone is pale yellow
   
   
   
   
3. compound adjectives made up of a noun, adjective, or adverb and a present participle whether used before or after the noun:
   
   
   far-reaching events
   the effects were far-reaching
   gold-bearing deposit
   north-trending fault
   the dyke is north-trending
   odd-looking feature
   
   
   but if the compound is preceded by an adjective modifying the first word in the compound, use two hyphens:
   
   
   mid-oceanic-ridge basalt
   north-northwest-trending striae
   light-green-weathering rocks
   
   
   
   
4. compound adjectives made up of a noun or adverb and a past participle when they precede the noun they modify:
   
   
   contact-metamorphosed sediment
   intrusion-hosted deposits
   ice-rafted material
   shear-zone-hosted deposits
   
   
   
   
5. compound adjectives when the adverb of the combination could be misread as the modifier of the noun:
   
   
   more-open creek bottoms
   shows much-improved growth
   
   
   
   
6. compound adjectives ending in an adverb of direction or place (in, out, up, down, etc.) when they precede the noun:
   
   
   built-up area
   ice break-up season
   rip-up clasts
   fining-upward cycles
   melt-out till
   trickle-down theory
   
   
   
   
7. compound adjectives made up of a preposition and a noun:
   
   
   in-house program
   per-day basis
   
   
   
   
8. where the meaning would not be clear without hyphens:
   
   
   elongated-clast fabric measurement
   stony, matrix-supported, subglacial till
   high sea-level beach
   subaqueous, sediment-flow deposit
   
   
   
9. compound adjectives that follow the noun in map legends:
   
   
   quartzite: white, thin-bedded, fine-grained, ripple-marked

Do not hyphenate the following:

1. compound adjectives that follow the noun modified (exceptions, see points 2, 3, and 9, above):
   
   
   The granite is coarse grained.
   The metamorphism is high grade.
   The sediments are contact metamorphosed.
   
   
   
2. adjectives used in the name of an institution or place:
   
   
   grand jury room
   school board members
   
   
   
   
3. compound adjectives made up of adjective and noun when both are capitalized:
   
   
   Safety First rules
   Merit Award survey
   
   
   
   
4. compound adjectives used in foreign expressions:
   
   
   in situ mining methods
   en échelon folding
   
   
   
   
5. if the adverb in a compound adjective cannot be misread as an adjective modifying the noun (the use of hyphens with adverbs ending in ly and with the adverb well are the most common errors):
   
   
   all too complacent attitude
   highly shattered rock
   carefully prepared samples
   poorly defined hypothesis
   equally productive means
   well developed feature
   glacially eroded landscape
   well known author
   thinly bedded limestone (prefer thin-bedded limestone)
   westerly draining rivers
   northerly trending faults
   
   
   
   
6. if the compound adjective is preceded by an adverb modifying the first word of the compound:
   
   
   a reasonably tall growing tree
   but a tall-growing tree
   
   
   
   
7. a two-word unit modifier, the first element of which is a comparative or superlative:
   
   
   best preserved specimen
   highest priced coal
   better drained soil
   larger sized grains
   
   
   
   
8. Chemical terms used as adjectives:
   
   
   calcium carbonate powder
   hydrogen sulphide solution
   

Phrases

Hyphenate in these cases:

1. many well known compounds:
   
   
   ball-and-pillow
   crag-and-tail
   cone-in-cone
   stoss-and-lee
   basin-and-dome
   topsy-turvy
   
   
   
   
2. compound phrases of more than two words, at least one of which is an adverb or preposition used as attributive adjectives:
   
   
   the cost-of-living index
   salt-and-pepper sandstone
   subject-by-subject analysis
   up-to-date approach
   

Prefixes

Hyphenate the following:

1. when the prefix is joined to a proper noun, unless usage demands otherwise:
   
   
   mid-Cretaceous
   pre-Wisconsinan
   neo-Gothic
   pro-Canadian
   trans-Arctic
   post-Tertiary
   mid-1980s
   but Subarctic, transatlantic, transpacific
   
   
   
   
2. expressions beginning with the prefixes ex (meaning 'former'), self, quasi, and all, where used to form adjectives or nouns, and those beginning with quasi used to form adjectives:
   
   
   all-inclusive
   self-assured
   ex-student
   self-control
   quasi-stellar
   self-possessed
   
   
   
   But do not hyphenate when self is the base word to which a suffix is added:
   
   
   selfish, selfless, selfsame

Do not hyphenate in these instances:

compounds with after, ante, anti, bi, co, counter, de, down, extra, infra, inter, intra, iso, macro, micro, multi, non, over, photo, poly, post, pre, pro, pseudo, re, retro, semi, stereo, sub, super, trans, tri, ultra, un, under, uni, and up, except where clarity demands otherwise:

Suffixes

Hyphenate the following:

Do not combine adjectives with like as in 'globularlike'. Write either globule-like or globular.

Numerals

Hyphenate in these cases:

1. compound numbers from twenty-one (twenty-first) to ninety-nine (ninety-ninth):
   
   
   Twenty-two trenches were cut through the overburden.
   
   
   
2. an adjectival compound in which one component is a cardinal number (one, two, three, etc.) and the other a noun or adjective:
   
   
   one-sided affair
   three-dimensional image
   two-person tent
   three-year-old maps
   
   
   Note
   
   
   two-rod rows (compound adjective and noun)
   two rod-rows (adjective and compound noun)
   
   
   
3. ordinal numbers (first, second, third, etc.) when they precede the word they modify:
   
   
   fifth-story room
   third-rate accommodation
   first-class assistant
   twenty-first-century technology
   
   
   
   
4. compounds of a number with odd:
   
   
   60-odd
   140-odd
   
   
   
   But write as one word compounds with fold and score:
   
   
   fourscore
   sixtyfold
   but 24-fold (because a compound number is used)
   

Do not hyphenate the following:

1. before a symbol that is not a letter:
   
   
   a 100°C thermometer
   27% salinity
   
   
   
   
2. between a cardinal numeral and a unit of measure:
   
   
   25 m section
   10 km traverse
   100 m cliff
   
   
   
   
3. between a unit of measure and the following adjective in a compound modifier:
   
   
   25 m thick section
   10 km long traverse
   5 m, 10 m, and 25 m thick beds
   100 m high cliff
   

Fractions

Hyphenate in these cases:

Do not hyphenate the following:

Suspended compounds

Hyphenate in these instances:

Compass points

Compass points consisting of two directions are written as one word:

Hyphenate after the first point when there are three points:

Single letters, figures, and signs

Hyphenate a letter, figure, or sign, and the word it modifies:

Do not hyphenate a unit modifier when the second element in the modifier is a letter or figure:

Element ratios

Hyphenate element ratios unless they involve isotopes: