Original paper
Flexible sandstone, a natural fiber composite material
Wirth, Richard
Neues Jahrbuch für Mineralogie - Abhandlungen Band 160 Heft 1 (1989), p. 93 - 103
13 references
published: Jan 19, 1989
ArtNo. ESP154016001004, Price: 29.00 €
Abstract
A characteristic feature of flexible sandstone is that if it is bent, the sandstone reaches a definite end point where the rigidity suddenly increases, Two structural features are typical for this investigated rock sample from Ouro Preto (Brazil) and its behavior. 1. The quartz grains are separated by crevasses of about 1 - 5/µm width (a common feature of flexible sandstone). 2. The sample consists of thin quartz layers (0.5 - 1 mm thickness) which are separated by fibrous layers of sillimanite, kyanite and white mica (a characteristic feature of this special sample). The cohesion of the flexible sandstone is achieved by a network-like intergrowth of the two Al2SiO5 modifications and some mica on the top and at the bottom of the quartz layers. This network mechanically stabilizes the individual quartz layers and links them together. The natural flexibility of sillimanite fibers in combination with the crevasses between the quartz grains result in pseudoductility. Thus, this special type of flexible sandstone can be called a natural fiber composite. The crevasses are suggested to be caused by hydraulic cracking of the rock by dehydration reactions during metamorphism.
Keywords
Sandstone • flexibility • fiber composite • grain boundary • dehydration • hydraulical cracking