Sedimentary - Museum of Stone Tools

Stone Type: Sedimentary

Sediments like sand, silt, and clay are produced by erosion of bedrock outcrops and accumulate in layers on land and under the oceans. The lower parts of these layered deposits become subjected to intense pressure and high temperatures. This compacts the sediments, forces out the water, and minerals such as silica precipitate into the spaces between particles. The particles are cemented together to form sedimentary rock.

Chert

Marine cherts sometimes contain fossils of organisms like diatoms and radiolarians, as well as sponge spicules. Petrified wood is a form of chert where the silica has replaced the structure of the fossil. The internal structure of chert is amorphous and lacks layering, which makes it ideal for stone-flaking. It occurs in a wide variety of colours, and most varieties respond well to heat-treatment to improve the material’s flaking characteristics. Chert is a general category which includes folk classifications like flint, chalcedony, opal, novaculite, porcellanite, and jasper, and many archaeologists prefer to use the folk classifications when describing artefacts.

Acheulean Handaxe

Angostura Point

Arrowhead Fetish

Aterian Point

Bead Blank

Bipolar Core

Blade

Burin

Caddo Biface

Clovis Point

Clovis Point

Eccentric

Elk River Point

Elko Point

End Scraper

Etley Point

Fan Scraper

Fasad Point

Flint

Flint occurs as nodules or seams in chalk. It is a folk classification within the general category of chert. Chert nodules form when tiny organisms extract pure silica from ocean water and use it as body armour or skeletons. When the organisms die, their skeletons dissolve and form a siliceous ooze, which eventually precipitates, coalesces, and recrystallises as the surrounding limestone rock is formed. When the material precipitates into hollows such as crustacean or mollusc burrows, nodules are formed. Fine-grained varieties of chert are some of the best stones for flintknapping because of the exceptionally high silica content.

The term ‘flint’ is often used interchangeably with chert in popular descriptions of stone tool-making. To further complicate the use of the term, some geologists use ‘flint’ to classify any dark grey to black chert, regardless of whether it derives from chalk deposits. Further, many European-trained archaeologists distinguish chert from flint based on quality, with ‘flint’ referring to the most siliceous variants and more grainy (and usually light-coloured) variants referred to as ‘chert’. Flint that occurs as nodules in chalk is coloured dark or medium grey, black, brown, reddish-brown, or off-white grey.

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe, ‘s-twist’

Barbed and Tanged Arrowhead

Barbed and Tanged Arrowhead

Blade

Blade Core

Burin

Core

End Scraper

Engraved Nodule

Eolith Core

Silcrete

Silcrete is a duricrust formed when quartz grains are cemented together by dissolved silica. In fine-grained silcrete, quartz sand grains appear to be ‘floating’ in the matrix of silica, while other varieties are composed mostly of quartz grains. The latter varieties are a form of orthoquartzite, or silicified sandstone. Silcrete is a very common source of stone for tools made by Aboriginal people in Australia, but it can also be found in other parts of the world, such as South Africa and the Congo Basin. The flaking quality of silcrete can often be improved by heat treatment.

Core on Flake

Core Tool

Flake

Grinding Dish

Horsehoof Core

Kimberley Point

Macroblade Core on Flake

Microblade

Microblade Core

Microlith

Modern Art, Mark Moore

Multiplatform Core

Pirri Point

Pirri Point

Quartzite

Acheulean Cleaver

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe

Acheulean Handaxe

Bifacial Core

Hammerstone

Kimberley Point

Levallois Core

Lupemban Foliate Biface

Lupemban Foliate Biface

Macroblade (Leilira) Knife

Macroblade Point

Macroblade Point

Spheroid

Stone-Tipped Spear

Waisted Axe

Mudstone

Mudstone is a fine-grained sedimentary rock formed from clays or muds. It consists mostly of silicate minerals. It differs from sandstone in having individual grains too small to see without a microscope. Mudstone differs from shale by its lack of parallel layers. Mudstone can be sufficiently silicified to be flaked into tools, and some varieties are suitable for heat-treatment. It tends to have a slightly rough or coarse texture, and occurs in a variety of colours depending on the trace minerals.

Blade

Dolomite

Stone Arm Ring

Sandstone

Sandstone is a sedimentary rock composed of sand grains (often quartz) bound together within a matrix of silt- or clay-sized particles. The stone’s abrasive qualities make it ideal for grinding stones, although the relative lack of silica in the matrix makes it difficult to flake in a controlled way. Harder and fine-grained varieties of sandstone have long been shaped by direct and indirect percussion flaking into building stones, or shaped by grinding into sculptures. Silicified sandstone can be flaked into tools if there is sufficient silica content in the matrix.