Spaced foliation planes are discrete, tabular domains separated by thin slabs of rock without fabric or with a differently oriented, older, primary (original) or secondary fabric. These rock slabs which are thick enough (> ca. 1mm) to be distinguished in hand specimens or outcrop are called microlithons.
The classic example of cleavage is mica, which cleaves in a single direction along the basal pinacoid, making the layers seem like pages in a book. In fact, mineralogists often refer to "books of mica".
Cleavage is a type of secondary foliation associated with fine grained rocks. For coarser grained rocks, schistosity is used to describe secondary foliation. There are a variety of definitions for cleavage, which may cause confusion and debate.
Cleavage is the property of a mineral that allows it to break smoothly along specific internal planes (called cleavage planes) when the mineral is struck sharply with a hammer. Fracture is the property of a mineral breaking in a more or less random pattern with no smooth planar surfaces.
Quartz has crystal surfaces but no cleavage at all. Fluorite forms cubic crystals like those of halite, but it cleaves along planes that differ in orientation from the crystal surfaces.
Cleavage is a type of rock layering or planar formation that forms within finely grained rocks due to deformation and metamorphism caused by heat and pressure. Specifically, cleavage is a type of foliation which is how geologists refer to certain types of deformed repeating layers that form within a metamorphic rock.
Cleavage: In mineral terms, cleavage describes how a crystal breaks when subject to stress on a particular plane. If part of a crystal breaks due to stress and the broken piece retains a smooth plane or crystal shape, the mineral has cleavage.
However, despite the fact that every mineral belongs to a specified crystal system, not every mineral exhibits cleavage. A mineral such as quartz may demonstrate beautiful, well-developed crystals and yet possess no distinct planes of cleavage.
In 1812, a man named Fredrich Mohs invented a scale of hardness called Mohs Scale which is still used today. He selected ten standard minerals, and arranged them in order of increasing hardness. Talc is the softest and diamond is the hardest. Each mineral can scratch only those below it on the scale.
Half of the earth's crust is composed of feldspar (plagioclase (39%) and alkali feldspar (12%)).
HCl. Pyrite has a hardness of 6-6.5 on the Mohs scale of hardness, which means it can scratch a fingernail but cannot scratch a glass plate. Pyrite does not react with dilute hydrochloric acid, meaning it does not effervesce or bubble when it comes into contact with the acid.
Diamond is formed in the cubic crystal system and has four perfect cleavage directions. A cleavage plane is the weakest direction in the molecular arrangement of the crystal. Diamonds are tougher in the directions where the atoms are bonded tightly together and less tough where they're not so tightly bonded.
Cleavage - The tendency of a mineral to break along flat planar surfaces as determined by the structure of its crystal lattice. These two-dimensional surfaces are known as cleavage planes and are caused by the alignment of weaker bonds between atoms in the crystal lattice.
Minerals that are bonded with equal strength in all directions, such as quartz, have no cleavage, but instead fracture to form irregular surfaces. These minerals break along curved surfaces to form conchoidal fractures, similar to what happens when glass breaks.
Foliation Controls How Rocks Break
Breaks along planes of weakness within a rock that are caused by foliation are referred to as rock cleavage, or just cleavage. This is distinct from cleavage in minerals because mineral cleavage happens between atoms within a mineral, but rock cleavage happens between minerals.
Quartz has no cleavage because it has equally strong Si–O bonds in all directions, and feldspar has two cleavages at 90° to each other (Figure 1.5). One of the main difficulties with recognizing and describing cleavage is that it is visible only in individual crystals.
The scale ranges from 1 (talc) which is scratched by all the other minerals, to 10 (diamond) which can scratch all of the other minerals.
For instance, depending on the trace amounts of impurities it contains, quartz may look colorless (no impurities), light pink (titanium, iron, or manganese), milky white (tiny bubbles of gas or liquid), purple (iron), yellow (iron), or brown (extra silicon).
Prismatic cleavage is cleavage parallel to a vertical prism {110}. Cerussite, tremolite and spodumene exhibit prismatic cleavage.
Pyrite. Mineral Type: No Cleavage. A metallic mineral that is pale brass-yellow in color, has 3 cleavage planes forming perfect cubes, produces a brown-black streak, has a hardness of 6.5 and a specific gravity of 5.0.
Parting: Some minerals which do not exhibit cleavage do have a characteristic that is similar, called parting. It occurs in minerals that are crystallographically twinned, or which have been stressed by pressure.
After fertilization, the development of a multicellular organism proceeds by a process called cleavage, a series of mitotic divisions whereby the enormous volume of egg cytoplasm is divided into numerous smaller, nucleated cells. These cleavage-stage cells are called blastomeres.