Stone Type: Metamorphic

Hardaway point 13

When layers of rock become deeply buried in the earth’s crust, intense pressure and high temperatures cause changes to the texture and mineral composition.  These ‘metamorphic’ changes occur without melting the rocks.  Metamorphic rocks usually have the same chemistry as the non-metamorphosed version, but differ in the types and sizes of the crystals that compose them.

Metasedimentary

Metasedimentary rock was first formed by the deposition and solidification of sediment. This sedimentary rock was then buried beneath other layers of rock and subjected to intense pressures and temperatures, causing the rock to recrystallise. This process hardens the stone and can make it suitable for flaking into tools.

Bidirectional core, Anaiwan

Bidirectional Core

Biface thinning flake Bletchington

Biface Thinning Flake

End scraper, North Carolina

End Scraper

Gunflint Nepal 1

Gunflint

screenshot (1)

Hafted Stone Axe

Macroblade Kimberley metased

Macroblade Point

Microblade core, Australia (2)

Microblade Core

Painted pebble, France

Painted Pebble

Pebble-edged core, Corindi Beach

Pebble-Edged Core

Pebble edge core Moonee Beach ARPA 1

Pebble-Edged Core

Pebble-edged core Moonee

Pebble-Edged Core

Engraved hammerstone, Scotland

Pilgrims Stone

River cobble in mesh bag

Power Stone

Adze, Thailand

Stone Adze

Axe from Ireland, AIA

Stone Axe

Axe blank Bletchington Pakr

Stone Axe Blank

Indonesian axe engraved

Stone Axe Talisman

Drill, North Carolina

Stone Drill

Metavolcanic

Metavolcanic rock was first formed by the deposition and solidification of deposits created in a volcanic eruption, such as basalt or volcanic ash. The volcanic layers were then buried beneath other layers of rock and subjected to intense pressures and temperatures, causing the rock to recrystallise. This process hardens the stone and can make it suitable for flaking into tools.

Clovis point 3, North Carolina

Clovis Point

Clovis point 2, North Carolina

Clovis Point

Large flake, Hat Head

Flake

Large backed flake

Flake Chopper

Stone axe, drilled, China

Fu Axe

Axe from Crescent Head

Grooved Stone Axe

Axe, Guilford NC 1

Guilford Axe

Axe, Guilford NC 2

Guilford Axe

Hafted adze PNG

Hafted Stone Adze

Axe, hafted in antler

Hafted Stone Axe

Hafted axe, Chile

Hafted Stone Axe

Hardaway point 13

Hardaway Side-Notched Point

Hardaway point 3

Hardaway Side-Notched Point

Hardaway point No. 1

Hardaway Side-Notched Point

Hardaway Point 2

Hardaway Side-Notched Point

Hardaway Dalton no 9

Hardaway-Dalton Point

Hardaway Dalton point 2

Hardaway-Dalton Point

Hardaway Dalton point 1

Hardaway-Dalton Point

Hardaway Dalton point 4

Hardaway-Dalton Point

Kirk corner-notched 3

Kirk Corner-Notched Point

Kirk corner-notched point 2

Kirk Corner-Notched Point

Kirk corner-notched point 3

Kirk Corner-Notched Point

Kirk corner-notched point 1 NC

Kirk Corner-Notched Point

Kirk Stemmed point 2

Kirk Stemmed Point

Silicified Tuff

Tuff is volcanic ash ejected from a volcano.  After it falls to the earth, it solidifies into rock by heat-induced fusion or through silicification.  Soft, coarse-grained tuff is not suitable for flaking, but hard, fine-grained varieties can be of excellent flaking quality.  The coarser varieties of tuff were sometimes used for sculptures or as building material.

Centripetal core Liang Bua 7

Centripetal Core

Soa core 3 conjoin

Centripetal Core

Liang Bua centripetal core re-do

Centripetal Core

Flake, Kobatuwa

Flake

Microblade core Australia, Nobby's chert

Microblade Core

Core 5 Soa basin

Multiplatform Core

Axe blank Manchester UK

Stone Axe Blank

Axe blank, England

Stone Axe Blank

Slate

Slate is a metamorphic rock formed when shale is compressed and baked.  The metamorphic process causes the the crystals to orient in the same direction, creating a planar structure in sheets of various thickness.  The planes can be separated into flat sheets.  Some types of slate can be percussion flaked provided the sheets are relatively thick and internally fused.  Most slate, however, is unsuitable for refined flaking because the stone splits along the planes rather than where the stoneworker wants the flakes to go.  Well-fused slates can be hammer dressed and are soft enough for grinding, and slate was often used for making sculptures, ornaments, and edge-ground axes.  In recent times, slate with pronounced planar structure was split into sheets to make pavers and roofing tiles.

Slate point 1

Adena Stemmed Point

Birdstone North Carolina

Birdstone

Gorget NC

Gorget

Hafted scraper, Alaska

Hafted Scraper

Axe blank, Czech Republic

Shaft-Hole Axe

Ulu 3, Alaska

Ulu

Ulu 2, Alaska

Ulu

Ulu, hafted

Ulu

Ulu with slot

Ulu

Argillite

Argillite is a fine-grained metasedimentary rock composed of clay particles.  It forms when a sedimentary clay or mud is cooked by exposure to intense heat and pressure within the Earth’s crust.  Argillite is intermediate between shale and slate, but it does not possess cleavage planes, which makes the dense and hard varieties suitable for stone tool-making.  Argillite and mudstone are similar in origin, texture, and knapping quality, but mudstones are not metamorphosed.  Argillite can occur in a variety of colours.

Engraved pebble, North Carolina

Engraved Pebble

Engraved pendant, USA

Engraved Pendant

Pipe, Indiana

Smoking Pipe

Cherty Hornfels

Hornfels forms when sedimentary or volcanic layers are baked from 300-800º C by an intruding mass of igneous magma, but at a relatively low pressure.  This contact metamorphism fuses the layers together and makes the stone suitable for flaking into tools.  Hornfels is usually dark brown or black.  Variants of the stone can resemble chert, although cherty hornfels is usually more coarse in texture.

Retouched flake Tasmania

Steep-Edged Scraper

Chlorite

Chlorite rock is formed by metamorphic processes.  The stone is composed of blue-green mica-like crystals.  The structure of the stone makes it unsuitable for flaking, but it can be pecked and ground into attractive objects.

Pipe chlorite North Carolina

Smoking Pipe

Jadeite

Nephrite and jadeite are green metamorphic rocks often referred to colloquially as ‘jade’.  Nephrite differs in crystal structure to jadeite.  Nephrite is known as a ‘amphibole’ mineral with oblique cleavage planes of about 120 degrees.  Jadeite is a ‘pyroxene’ mineral with cleavage planes of about 90 degrees.  Nephrite is less dense than jadeite and has a less vitreous lustre.  Both minerals are exceptionally tough because they are made up of interwoven fibre-like crystals.  Because of their crystal structures, nephrite and jadeite are unsuitable for flaking.  However, they can be shaped by sawing and grinding, followed by polishing.  Nephrite and jadeite were highly desired for their green colour and these stones had sacred connotations in many parts of the world.  The materials are perhaps most familiar as sculptures and jewellery, but stone axes were often made from them.  Their exceptional hardness allowed the materials to be grounded and polished to an exceptionally sharp cutting edge.  

Jadeite pendant Russia

Pendant

Stone axe, Zug, Switzerland

Stone Axe

Soapstone

Soapstone, or steatite, is a soft metamorphic rock composed primarily of talc. It is usually gray, bluish, green, or brown in colour, and has a ‘soapy’ texture. Soapstone is easily carved and was a popular material for a variety of vessel forms and symbolic or decorative objects world-wide. It has an usual ability to absorb, hold, and radiate heat, and was often used as shaft-straighteners, pipes, boiling stones, and cooking pots.

Soft stone bowl with lugs NC

Soapstone Bowl

Soft stone bowl NC Warren Wilson

Soapstone Bowl

Soft stone bowl, UAE

Soapstone Bowl

Nephrite

Nephrite and jadeite are green metamorphic rocks often referred to colloquially as ‘jade’. Nephrite differs in crystal structure to jadeite. Nephrite is known as a ‘amphibole’ mineral with oblique cleavage planes of about 120 degrees. Jadeite is a ‘pyroxene’ mineral with cleavage planes of about 90 degrees. Nephrite is less dense than jadeite and has a less vitreous lustre. Both minerals are exceptionally tough because they are made up of interwoven fibre-like crystals. Because of their crystal structures, nephrite and jadeite are unsuitable for flaking. However, they can be shaped by sawing and grinding, followed by polishing. Nephrite and jadeite were highly desired for their green colour and these stones had sacred connotations in many parts of the world. The materials are perhaps most familiar as sculptures and jewellery, but stone axes were often made from them. Their exceptional hardness allowed the materials to be grounded and polished to an exceptionally sharp cutting edge.

Adze NZ jade updated

Stone Adze