Conglomerate

Conglomerate is a sedimentary rock formed from rounded gravel and boulder sized clasts cemented together in a matrix. The rounding of the clasts indicates that they have been transported some distance from their original source (e.g. by a river or glacier), or that they have resided in a high energy environment for some time (e.g. on a beach subject to wave action). The cement that binds the clasts is generally one of either calcite, silica or iron oxide. The matrix can consist solely of the cementing material, but may also contain sand and / or silt sized clasts cemented together among the coarser clasts.

Conglomerates can be further divided in:

• Clast supported (Orthoconglomerates): where the clasts touch each other and the matrix fills the voids; and
• Matrix supported (Paraconglomerates) : consist of a clast-supported rock with less than 15% matrix of sand and finer particles. The clasts are not in contact and the matrix surrounds each clast.

a conglomerate where the clasts represent more than one rock type is termed polymictic (or petromictic), while one where the clasts are of a single rock type are monomictic (or oligomictic). Conglomerate forms in a very energetic environment, where rocks are eroded and carried downhill so swiftly that they aren't fully broken down into sand.

Conglomerate classification diagram

conglomerate sample. From Natalie Teager, Arizona State University.

conglomerate sample. Salt River, Phoenix (Arizona). From Natalie Teager, Arizona State University.

Bibliography

• E. WM. Heinrich (1956): Microscopic Petrografy. Mcgraw-hill book company,inc
• M. J. Hibbard (1994): Petrography to Petrogenesis. Prentice Hall editore

Photo
Rounded clasts (sedimentary, volcanic) fragments in a Conglomerate. Italy. PPL image, 2x (Field of view = 7mm)	Rounded clasts (sedimentary, volcanic) fragments in a Conglomerate. Note the two pyroxene crystals. Italy. XPL image, 2x (Field of view = 7mm)	Rounded clasts (sedimentary, volcanic) fragments in a Conglomerate. Italy. XPL image, 2x (Field of view = 7mm)
Rounded clasts (sedimentary, volcanic) fragments in a Conglomerate. Italy. PPL image, 2x (Field of view = 7mm)	Rounded clasts (sedimentary, volcanic) fragments in a Conglomerate. Italy. XPL image, 2x (Field of view = 7mm)	Rounded clasts (sedimentary, volcanic) fragments in a Conglomerate. Note the calcite filling a void. Italy. PPL image, 10x (Field of view = 2mm)
Rounded clasts (Bioclast and sedimentary) fragments in a Conglomerate. Italy. PPL image, 10x (Field of view = 2mm)	Rounded clasts (Bioclast and sedimentary) fragments in a Conglomerate. Italy. PPL image, 10x (Field of view = 2mm)	Rounded clasts (Bioclast and sedimentary) fragments in a Conglomerate. Italy. PPL image, 10x (Field of view = 2mm)
Rounded clasts (Bioclast and sedimentary) fragments in a Conglomerate. Italy. XPL image, 10x (Field of view = 2mm)	Rounded clasts (Bioclast and sedimentary) fragments in a Conglomerate. Italy. PPL image, 10x (Field of view = 2mm)	Rounded clasts (Bioclast and sedimentary) fragments in a Conglomerate. To the right there is a big serpentinite fragment with brown spinel. Italy. PPL image, 10x (Field of view = 2mm)
Rounded clasts (Bioclast and sedimentary) fragments in a Conglomerate. To the right there is a big serpentinite fragment with spinel. Italy. XPL image, 10x (Field of view = 2mm)	Rounded clasts (sedimentary, volcanic) fragments in a Conglomerate. Note the serpentinite clasts. Italy. PPL image, 2x (Field of view = 7mm)	Rounded clasts (sedimentary, volcanic) fragments in a Conglomerate. Note the serpentinite clasts (Yellow). Italy. PPL image, 2x (Field of view = 7mm)
Rounded clasts (sedimentary, metamorphic and volcanic) fragments in a Conglomerate. Italy. XPL image, 2x (Field of view = 7mm)	Rounded clasts (sedimentary, metamorphic and volcanic) fragments in a Conglomerate. Italy. XPL image, 10x (Field of view = 2mm)	Rounded clasts (sedimentary, metamorphic and volcanic) fragments in a Conglomerate. Note the skeletal plagioclase within a volcanic clast. Italy. PPL image, 2x (Field of view = 7mm)
Rounded clasts (sedimentary, metamorphic and volcanic) fragments in a Conglomerate. Note the skeletal plagioclase within a volcanic clast. Italy. XPL image, 2x (Field of view = 7mm)	skeletal plagioclase within a volcanic clast. XPL image, 10x (Field of view = 2mm)	Rounded clasts in a fine-grainded matrix. PPL image, 2x (Field of view = 7mm)
Rounded clasts in a fine-grainded matrix. PPL image, 2x (Field of view = 7mm)	Rounded clasts in a fine-grainded matrix. PPL image, 2x (Field of view = 7mm)	Rounded clasts in a fine-grainded matrix. PPL image, 2x (Field of view = 7mm)
Rounded clasts in a fine-grainded matrix. PPL image, 2x (Field of view = 7mm)