Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Metasandstone is a metamorphic rock derived from sandstone. It is characterized by a predominantly quartzose composition, where the original detrital quartz grains have undergone recrystallization and often intergrowth, resulting in a tougher, more cohesive rock than its protolith. The degree of metamorphism dictates the extent of recrystallization and the obliteration of original sedimentary features. It typically exhibits a granoblastic texture, meaning it is composed of interlocking, equidimensional grains. While often massive, some metasandstones can show relict bedding or, under higher strain, a weak foliation.
How to Identify
- Color
- Typically light-colored, ranging from white, gray, and tan to reddish-brown, depending on the purity of the quartz and the presence of minor accessory minerals or iron oxides.
- Luster
- Vitreous (glassy) to dull, depending on the grain size and degree of recrystallization.
- Texture
- Granoblastic, with interlocking, equidimensional grains. Original clastic texture may be partially preserved or completely obliterated. Can be fine-grained to coarse-grained. May feel gritty if grains are not fully intergrown.
- Crystal Form
- Individual quartz grains are anhedral (lacking well-formed crystal faces) due to recrystallization and intergrowth.
- Cleavage
- No true cleavage; fractures conchoidally or irregularly across grain boundaries. Unlike sandstone, it typically breaks through the quartz grains rather than around them.
- Geological Environment
- Formed in regional metamorphic settings (e.g., orogenic belts, continental collision zones) or contact metamorphic aureoles where sandstones are subjected to elevated temperatures and pressures. Often found in association with other metamorphic rocks like schists, gneisses, and slates.
Key Facts
- Hardness: 7 (Mohs scale, due to quartz content)
- Specific Gravity: 2.65 - 2.70 g/cm³
- Crystal System: Trigonal (for quartz, the dominant mineral)
- Color: White, gray, tan, reddish-brown, sometimes green or purple due to impurities.
- Luster: Vitreous to dull
- Transparency: Opaque to translucent (in thin sections or very fine-grained varieties)
- Fracture: Conchoidal to irregular, often breaking across grains.
- Cleavage: None (for the rock as a whole; quartz has poor to indistinct cleavage)
- Composition: Predominantly quartz (SiO₂), typically >90%. Minor amounts of feldspar, mica (muscovite, biotite), chlorite, iron oxides, and other accessory minerals may be present.
Quick Check
- Color: White, gray, tan, reddish-brown
- Luster: Vitreous to dull
- Streak: White
Physical Characteristics
- Crystal Habit: Granoblastic, interlocking anhedral grains of quartz.
- Cleavage Type: Absent in the rock; quartz has poor to indistinct cleavage.
- Fracture Type: Conchoidal to irregular.
- Tenacity: Brittle, very tough.
- Luster Type: Vitreous to dull.
Formation
Metasandstone forms from the metamorphism of sandstone. This process involves recrystallization of quartz grains and cement under elevated temperatures and pressures, typically without significant foliation development unless subjected to high differential stress. The original clastic texture of the sandstone may be partially or completely obliterated, leading to a more interlocking, crystalline fabric. The degree of metamorphism can range from low-grade (e.g., diagenesis to anchimetamorphism) to high-grade (e.g., amphibolite or granulite facies).
Usage
Metasandstone is primarily used as a construction material, including dimension stone, aggregate for concrete and road construction, and railway ballast. Its durability and resistance to weathering make it suitable for these applications. High-purity metasandstone (metaquartzite) can be used in the production of silica refractories, ferrosilicon, and as a flux in metallurgical processes.
Age Distribution
Ranges from Precambrian to Cenozoic, depending on the age of the protolith sandstone and the timing of metamorphism.
Where to Find
Appalachian Mountains, USA
Extensive occurrences of metasandstone and quartzite are found throughout the Appalachian orogen, particularly in the Blue Ridge and Valley and Ridge provinces, where ancient sandstones have been metamorphosed during multiple orogenic events.
Scottish Highlands, UK
Significant exposures of metasandstone, often referred to as quartzite, are present in the Scottish Highlands, part of the Caledonian orogen.
Canadian Shield, Canada
Large areas of the Canadian Shield contain ancient metasandstones and quartzites, representing metamorphosed sedimentary sequences from the Precambrian.
Himalayan Orogen, Asia
Metasandstones are common in the Himalayan mountain range, where extensive sedimentary sequences have been subjected to intense regional metamorphism during the collision of the Indian and Eurasian plates.
Brazil
Various regions in Brazil, particularly within Precambrian shield areas, host significant deposits of metasandstone and quartzite.
Finding Tips
Look for Metamorphic Terranes
Metasandstone is found in regions that have undergone significant metamorphism, such as ancient mountain belts, cratonic margins, and areas affected by regional or contact metamorphism.
Examine Outcrops for Hardness and Texture
Test the rock's hardness; metasandstone is very hard (Mohs 7). Look for a sugary, interlocking texture where individual grains are difficult to distinguish or break across rather than around.
Check for Relict Sedimentary Structures
While often massive, some metasandstones may retain relict bedding planes or cross-bedding from their sandstone protolith, which can help in identification.
Distinguish from Sandstone
A key differentiator from sandstone is that metasandstone will typically break through the quartz grains, creating a smoother, more conchoidal fracture surface, whereas sandstone tends to break around the grains, leaving a rougher, more friable surface.
Similar Rocks
Quartzite
Quartzite
Also known as: Metaquartzite
Sandstone
Sandstone
Also known as: Arenite
Arkose
Arkose
Also known as: Feldspathic Sandstone
Greywacke
Greywacke
Also known as: Dirty Sandstone
Scientific Classification
- Mineral Class
- Silicate (for quartz)
- Group
- Metamorphic Rock
- Crystal System
- Trigonal (for quartz)
- Chemical Formula
- SiO₂ (predominant, as quartz)
- Composition
- Primarily quartz (SiO₂), with minor amounts of other minerals depending on the protolith and metamorphic conditions.
Explore Metasandstone
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.