Glassy texture Similar to ordinary glass. Aphanitic, even or porphyritic
Colour
Black – N1 Combination green and black
Mineral Composition
Rhyolite Iron oxide - how this volcanic glass receives its color of black. Volcanic glass with a composition similar to basalt and gabbro
Chemical composition
Silica (about 65 to 80 percent) Low in water Has similar composition to rhyolite and granite
Origin
Along the edges of lava flow (extrusive) Along the edges of a sill or a dykes (intrusive) Where lava contacts water (extrusive) Where lava cools while air bone (extrusive) Formed as an extrusive rock and cools rapidly that’s atoms unable to arrange themselves into a crystalline structure.
Fossil Limestone (Sedimentary rock)
Most of these rocks are formed of materials which have been moved from their place of origin to the present site of deposition. Sedimentary layers form slowly, usually over millions of years.
Colour
Very light grey – N8 Grey through yellow.
Texture
Bioclastic (crystalline) Mix of clastic materials and calcitic shells clastic or non-clastic.
Mineral composition
Composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite more than 50% calcium carbonate (calcite - CaCO3)
Chemical composition
Precipitation of calcium carbonate from lake or ocean water. Calcite readily reacts with a small drop of HCl.(gaseous and cloudy)
Origin
Occurs in areas underlain by sedimentary rocks Biochemical Sediment is deposited in a number of environments of deposition, by both moving air and moving water. As a filter stone in on-site sewage disposal systems.
Used as a construction material
Uses
Used as crushed stone for road base and railroad ballast Powdered limestone is also used as a sorbent (a substance that absorbs pollutants) at many coal-burning facilities
Gneiss (Metamorphic Rock)
Widely distributed type of rock formed by high-grade regional metamorphic process Change of form
Texture
Foliated texture A broad term referring to the alignment of sheet-like minerals Compositional banding due to segregation of minerals
Colour
Medium light grey
Mineral composition
Quartz Potassium feldspar Sodium feldspar
Chemical composition
High in silica content Medium- to coarse foliated
Origin
Characterized by bending caused by segregation of different types of rock Typically light and dark silicates Mostly elongated and granular structures rather than sheets or plates Form from the metamorphism of granite or diorite