Rock
Amphibolite
Amfibolit
A dark, heavy, salt-and-pepper metamorphic rock: basalt or gabbro transformed at depth; the stone of Neolithic axes.
- Popularly: Natural stone (building and decor)
- Building stone
In short
Amphibolite is a dark, dense metamorphic rock made mainly of amphibole (mostly hornblende) and plagioclase feldspar. It usually forms when dark igneous rocks such as basalt or gabbro are transformed deep in the crust at temperatures above about 500 °C. Being hard and taking a good polish, it is used as building stone; prehistoric people also made axes and adzes from it.
Photos
How does it form?
Amphibolite is a medium- to high-grade metamorphic rock. It forms mostly when dark igneous rocks such as basalt and gabbro, and sometimes clay-rich limestones (marls) or dolomitic sediments, are transformed in the crust at temperatures above about 500 °C (and pressures below about 1.2 GPa). These conditions are called the “amphibolite facies”: the minerals in the rock recrystallise, hornblende and plagioclase grow, and the rock takes on a dark, dense look.
If heat and pressure rise further, amphibolite may turn into granulite, or, under very high pressure, into eclogite.
What is it used for?
- Building and cladding stone: Its dark colour, hardness and good polish make it suitable for paving, building facades and interior decoration.
- Prehistoric tools: Amphibolite and similar amphibole-rich rocks were preferred for polished axes and adzes in the early Neolithic of Central Europe.
- Science: Amphibolite is studied to understand the deep roots of old mountain belts and the history of the oldest continental crust.
In Türkiye
In Türkiye, amphibolite occurs among the high-grade rocks of the Kazdağ Massif in north-western Anatolia. The lowest unit of the massif, the Fındıklı formation, consists of amphibole-gneiss, marble and a little amphibolite; the overlying Tozlu formation consists of metadunite and orthoamphibolite; and the uppermost Sutuven formation contains sillimanite-gneiss and migmatite with a little amphibolite.
What determines its value?
Amphibolite is abundant and is mostly used cheaply as crushed stone or road base. As building and cladding stone, its value depends on dark colour and even texture, on how well it polishes, on its strength, on whether large crack-free blocks can be quarried, and on the distance of the quarry. Garnet-bearing or boldly patterned kinds are more sought after for decorative uses.
This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.
How to recognise it
- 1
It is a dark, greenish-black, heavy and dense stone; black amphibole and white plagioclase grains give a “salt-and-pepper” look.
- 2
The amphibole crystals are weakly aligned, so the rock shows a faint streaking or banding.
- 3
A steel knife scratches it only with difficulty, and it cannot scratch glass.
- 4
It does not fizz in vinegar or dilute acid and does not attract a magnet.
- 5
In some, reddish garnet crystals stand out on the dark background.
Fakes and imitations
What shops usually don’t tell you:
- It is confused with dark igneous rocks such as basalt and gabbro; in amphibolite the crystals are weakly aligned and the grains can be seen by eye. The locality and the minerals found with it often decide it.
- In the trade amphibolite is often sold as “granite”; garnet amphibolite, for example, is on the market as “Nordic Sunset Granite”.
- Hornblendite, an igneous rock made almost entirely of amphibole, also resembles amphibolite.
Myths and misconceptions
MythAmphibolite and amphibole are the same thing.
FactAmphibole is a group of minerals such as hornblende; amphibolite is a rock made mainly of amphibole and plagioclase.
MythDark stones sold as “granite” are real granite.
FactIn the natural stone trade the name granite is used broadly; some stones, such as the garnet-bearing one sold as “Nordic Sunset Granite”, are in fact amphibolite.
Did you know?
Central Europe's first farmers (about 5400–5000 BC, the Linear Pottery culture) made polished axes and adzes from the amphibole-rich metabasite of the Jizera Mountains in northern Bohemia, and these tools were carried far and wide.
The Isua belt in south-western Greenland is about 3.7–3.8 billion years old, and much of it consists of amphibolite metamorphosed from basalt.
Where is it found?
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- Jistebsko, Jizera Mountains, Czechia · Historic sourceHere lie the Neolithic quarries of an amphibole-rich metabasite from which polished axes and adzes were made and distributed across Central Europe.
- Libodřice, Kolín District, Czechia · Known localityAmphibolite is quarried at the south-western edge of the village; the rock contains garnet and zones rich in epidote, clinozoisite and diopside.
- Isua Greenstone Belt, southwestern Greenland · Known localityAbout 150 km north-east of Nuuk, this 3.7–3.8 billion-year-old belt consists mainly of amphibolite metamorphosed from basalt.
- Around the Trift Glacier, Bern, Switzerland · Known localityNear the glacier, blocks of dark amphibolite mingled with light granitic bands can be seen.
- Murmansk area, Kola Peninsula, Russia · Known localityThe garnet amphibolite sold as “Nordic Sunset Granite” is reported to come from this area; despite the name it is amphibolite, not granite.
- Kazdağ Massif, Balıkesir–Çanakkale, Türkiye · Known localityThe high-grade rocks of the massif include amphibolite and orthoamphibolite, together with gneiss and marble.
Locations are approximate to protect sites. Red dots mark places in Türkiye. Open in the big map →
Frequently asked questions
What is amphibolite?
Amphibolite is a dark, dense metamorphic rock made mainly of amphibole (mostly hornblende) and plagioclase feldspar. It usually forms when dark igneous rocks such as basalt or gabbro are transformed deep in the crust at temperatures above about 500 °C. Being hard and taking a good polish, it is used as building stone; prehistoric people also made axes and adzes from it.
What is amphibolite used for?
Building and cladding stone: Its dark colour, hardness and good polish make it suitable for paving, building facades and interior decoration. Prehistoric tools: Amphibolite and similar amphibole-rich rocks were preferred for polished axes and adzes in the early Neolithic of Central Europe. Science: Amphibolite is studied to understand the deep roots of old mountain belts and the history of the oldest continental crust.
How hard is amphibolite?
It has a hardness of 5–6 on the Mohs scale. It can scratch glass; a steel knife scratches it only with difficulty. Its specific gravity is 2.9–3.1 g/cm³.
Where is amphibolite found?
Its best-known localities: Jistebsko, Jizera Mountains, Czechia; Libodřice, Kolín District, Czechia; Isua Greenstone Belt, southwestern Greenland; Around the Trift Glacier, Bern, Switzerland; Murmansk area, Kola Peninsula, Russia.
Where is amphibolite found in Türkiye?
Known localities in Türkiye: Kazdağ Massif, Balıkesir–Çanakkale, Türkiye.
How can you tell if amphibolite is real?
It is a dark, greenish-black, heavy and dense stone; black amphibole and white plagioclase grains give a “salt-and-pepper” look. The amphibole crystals are weakly aligned, so the rock shows a faint streaking or banding. A steel knife scratches it only with difficulty, and it cannot scratch glass. It is confused with dark igneous rocks such as basalt and gabbro; in amphibolite the crystals are weakly aligned and the grains can be seen by eye. The locality and the minerals found with it often decide it.
Is amphibolite valuable?
On the “street to diamond” value ladder it sits on step 2 of nine: Raw material by the tonne. Amphibolite is abundant and is mostly used cheaply as crushed stone or road base. As building and cladding stone, its value depends on dark colour and even texture, on how well it polishes, on its strength, on whether large crack-free blocks can be quarried, and on the distance of the quarry. Garnet-bearing or boldly patterned kinds are more sought after for decorative uses.
Sources
- Amphibolite · Wikipedia
- Amfibolit · Vikipedi
- Amphibolite · Encyclopaedia Britannica
- Amphibolite: Identification, Properties & Lookalikes · Rockhounding.org
- Amphibolite density data (W. P. Clement) · University of Massachusetts Amherst
- Prehistoric quarrying in the Jizerské hory Mountains (Burgert, Šída, Trampota, Kachlík & Přichystal) · Archeologia Polski 69, 2024
- Libodřice · Wikipedia
- Libodřice – lom (quarry) · Czech Geological Survey, Geological localities
- Isua Greenstone Belt · Wikipedia
- Trift Glacier · Wikipedia
- New Results on the Lithostratigraphy of the Kazdağ Massif in Northwest Turkey (Duru, Pehlivan, Şentürk, Yavaş & Kar) · Turkish Journal of Earth Sciences 13 (2), 2004
- Kaz Dağı (Mount Ida) · Wikipedia
External links
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