My Pet Rock Gideon The Gabbro

By: Nathan Mendes

Type of Rock

Specific name: Gabbronorite

Rock Type: Igneous


Gabbro is composed of calcium plagioclase, pyroxene, and minor olivine, but no quartz. Also, Gabbro is non-foliated.


Gabbro refers to a large group of dark, often coarse-grained, mafic-intrusive rocks chemically equivalent to basalt. It forms when molten magma is trapped beneath the Earths surface and slowly cools into a holocrystalline mass.


It is often mentioned that the term “gabbro” was brought into geological terminology by a German geologist Leopold von Buch. The term itself comes from Italy. Von Buch redefined the term in 1810 as a rock composed of diallage and feldspar or saussurite. Saussurite is a mixture of epidote, albite, and other alteration minerals. Saussuritized versions can be named metagabbro nowadays because its original composition has clearly been altered by metamorphism. Much of the Earth's oceanic crust is made of gabbro, formed at mid-ocean ridges. Gabbro is also found as plutons associated with continental volcanism. Due to its variant nature, the term "gabbro" may be applied loosely to a wide range of intrusive rocks, many of which are merely "gabbroic".

Place In The Rock Cycle

Gideon's place in the rock cycle is when magma cools slowly, very deep underground. Large crystals then are formed. He is an intrusive igneous rock because he forms from magma underground.

Practical Uses

Gabbro is used as...

  • Aggregate, fill etc. in the construction and roading industries.
  • Cut and polished for dimension stone (called black granite.)
  • For building facings, foyers etc.
  • Facing stone
  • Sea Defenses
  • Flooring and worktops
  • Monumental stone

Works Cited

Alden, A. (n.d.). Igneous rock types. Retrieved December 23, 2015, from About

Education website: htp://


Bitesize. (2014). The rock cycle. Retrieved January 3, 2016, from BBC website:



Gabbro. (n.d.). Retrieved January 3, 2016, from UCL website:



The University of Auckland. (2005). Gabbro. Retrieved January 3, 2016, from

Flexible Learning website: htps://