Figure \(\PageIndex{9}\): Citrine, a variety of quartz showing conchoidal fracture. For example, quartz and olivine rarely show cleavage and typically break into conchoidal fracture patterns. The mineral olivine (/ ˈ ɒ l ɪ ˌ v iː n /) is a magnesium iron silicate with the formula (Mg 2+, Fe 2+) 2 Si O 4.Thus, it is a type of nesosilicate or orthosilicate.The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickly on the surface.. The Plagioclase series is a group of related feldspar minerals that essentially have the same formula but vary in their percentage of sodium and calcium. Olivine shows no cleavage planes, only irregular to conchoidal fracture. Olivine, any member of a group of common magnesium, iron silicate minerals.. General considerations. If present in crystal form, epidote forms elongated crystals with one perfect cleavage that is quite distinct from olivine’s typical granular crystal habit. Olivine is very susceptible to alteration and often has a brownish weathering rind of assorted clay minerals. OLIVINE (peridot) BACKGROUND INFORMATION. Olivine Olivine is a simple orthosilicate in which the SiO 4 tetrahedra are independent of each other. Click here to go back to the main page. Olivine is a solid solution series mineral whose two most common end members are forsterite (Mg) and fayalite (Fe). This page concerns itself with olivine in general. If you need end member-specific information, please see the forsterite and fayalite pages. Cleavage and Fracture. Olivines are an important rock-forming mineral group. Magnesium-rich olivines are abundant in low-silica mafic and ultramafic igneous rocks and are believed to be the most abundant constituent of the Earth’s upper mantle. Peridot is a gem variety of the olivine mineral group. Cleavage is the tendency of a mineral to break along smooth planes parallel to zones of weak bonding. Fracture is the tendency of a mineral to break along curved surfaces without a definite shape. Albite and Anorthite are the end members of the series, with the intermediary minerals Oligoclase, Andesine, Labradorite, and Bytownite. Transparent to translucent epidote crystals are also strongly pleochroic, which means that their color changes (from green to brown) as they are rotated in light. Cleavage: poor on {010} and {110}, {010} ... Fracture: conchoidal Streak: colorless Return to the Index of Peridot Mineral Information. Talc Gypsum Calcite Fluorite Apatite Luster (M/NM) Color Hardness (1-10) Cleavage/Fracture Crystal Form Streak Specific Gravity Diagnostic Properties Chemical Group Uses Potassium Feldspar (Orthoclase) Quartz Corundum Galena Olivine Luster (M/NM) Color Hardness (1-10) Cleavage/Fracture Crystal Form Streak Specific Gravity Diagnostic Properties Chemical Group Uses These minerals do not have planes of weakness and break irregularly. olivine, biotite How does mineral cleavage differ from mineral fracture? It is a solid solution of the end-members forsterite (Mg 2 SiO 4) and fayalite (Fe 2 SiO 4), although most examples are closer to the forsterite end-member. Olivine Crystallography: Axial Ratios: a:b:c =0.4663:1:0.6146 : Cell Dimensions: a = 4.78, b = 10.25, c = 6.3, Z = 4; V = 308.67 Den(Calc)= 3.30 Figure \(\PageIndex{10}\): Graphite showing layers of carbon atoms separated by a gap with weak bonds holding the layers together. Mineral cleavage is the mineral's tendency to break along flat, even planes, whereas mineral fracture is the …