Systematics: Lunar Rock Classification

International Union of Geological Sciences
Subcommission on the Systematics of Igneous Rocks (2001)

I. SEDIMENTARY (RegolithMixture of unconsolidated rocky fragments, soil, dust and other fine granular particles blanketing the surface of a body lacking an atmosphere. Regolith is the product of "gardening" by repeated meteorite impacts, and thermal processes (such as repeated heating and cooling cycles).  )

II. METAMORPHICRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment.

A. Shocked (monomict and polymict) rocks B. Impact (melt) breccias and glasses

III. IGNEOUS

A. Mare-type
1. Crystalline
a. Ti-poor basaltBasalt is the most common extrusive igneous rock on the terrestrial planets. For example, more than 90% of all volcanic rock on Earth is basalt. The term basalt is applied to most low viscosity dark silicate lavas, regardless of composition. Basalt is a mafic, extrusive and fine grained igneous rock (<1.5 wt% TiO2) [formerly VLT] b. Medium Ti basalt (1.5–6 wt% TiO2) [formerly low-Ti] c. Ti-rich basalt (>6 wt% TiO2) [formerly high-Ti] 2. Glassy
a. Green
b. Yellow
c. Orange
d. Red
e. Black
B. Highland-type
1. Coarse-grained (>3 mm) [and transitional types]
a. AnorthositeA phaneritic, intrusive igneous rock made with a modal composition (i.e. volume%) > 90% plagioclase feldspar of undefined composition (anorthitic to albitic, or combination thereof), and a small mafic component between 0 - 10% such as pyroxene, ilmenite, magnetite, and olivine 1. The name anorthosite is derived from the calcium-rich
b. NoriteIgneous rock composed of 90% plagioclase, 95% orthopyroxene (low-Ca pyroxene) and less than 10% olivine. Norite is most commonly found in the lunar (highlands) meteorites but has also been found in about a dozen diogenites, a few shergottites, and a very small number of other achondrite types. Gabbro is very
c. GabbroWork in progress Coarse-grained igneous rock of basaltic composition that formed at depth and is 90% plagioclase. clinopyroxene, https://www.sandatlas.org/gabbro/ The most important mineral groups that make up this rock type are plagioclase and pyroxene. Plagioclase usually predominates over pyroxene. Plagioclase is sodium-calcium feldspar. It contains more calcium than sodium in gabbro. If there is
d. TroctoliteTroctolite is an intrusive igneous rock consisting of plagioclase feldspar and olivine. It is a member of gabbroic rocks family. It is compositionally similar to gabbro. The main difference is that it does not contain pyroxene or contains very little while it is a major mineral in gabbro. It can
e. Dunite
2. Fine-grained (<3 mm)
a. Felsite
b. KREEPLunar igneous rock rich in potassium (K), rare-earth elements (REE), phosphorus (P), thorium, and other incompatible elements. These elements are not incorporated into common rock-forming minerals during magma crystallization, and become enriched in the residual magma and the rocks that ultimately crystallize from it. basalt
3. Fragmental (see II. above if metamorphic)