hornblende, calcium-rich amphibole mineral that is monoclinic in crystal structure. Hornblende occurs widely in metamorphic and igneous rocks. Pargasite occurs in high-grade metamorphic rocks that tend to have more aluminum. Metamorphic rocks with abundant hornblende are called amphibolites.
What is hornblende gneiss?
Gneiss is a widespread metamorphic rock that is medium to coarse grained and often contains significant amounts of quartz and feldspar. A gneiss in which the dark green or black amphibole mineral hornblende is largely responsible for the dark coloration is typically referred to as a hornblende gneiss. …
What is hornblende mineral used for?
Its primary use might be as a mineral specimen. However, hornblende is the most abundant mineral in a rock known as amphibolite which has a large number of uses. It is crushed and used for highway construction and as railroad ballast. It is cut for use as dimension stone.
What is unique about hornblende?
Hornblende has a hardness of 5–6, a specific gravity of 2.9–3.4 and is typically an opaque green, greenish-brown, brown or black color. Its planes of cleavage intersect at 56° and 124° angles.
What is the difference between tourmaline and hornblende?
Tourmaline is distinguished from biotite and hornblende by the absence of cleavage, the presence of striated prisms, and (for hornblende) parallel extinction. Lighter colored tourmalines can be confused with topaz, apatite or corundum, but can be distinguished by certain optical properties.
Is hornblende a gemstone?
In the gem industry, hornblende is mostly famous for being an impurity included in other gemstones, but on rare occasion, some especially fine hornblende crystals may be cut and polished as gemstones.
Where is hornblende found in the US?
Hornblende is a metamorphic rock and can be mixed with Feldspar, Quartz or Mica to form Granite. It also occurs as dark crystals in Marble. Hornblende deposits are located in near Mount Vesuvius and in Norway, Sweden, Italy, Canada (Ontario) and the United States (Massachusetts, New Hampshire, New Jersey, New York).
How do you identify hornblende in a thin section?
In PPL a thin section of Hornblende ranges from yellow -green to dark brown. Green varieties usually have X= light yellow green, Y=green or grey-green and Z=dark green. Brownish varieties have X=greenish-yelow/brown, Y=yellowish to reddish brown and Z=grey to dark brown.
How do you identify apatite in the thin section?
Due to the phosphate content, apatite crystals are usually small and can be hard to detect in thin section. The apatite crystal is very small and elongated. Its high relief allows it to stick out from the other colorless minerals. Under cross-polars apatite exhibits a first order gray color.
Where is hornblende found on Earth?
Hornblende is a very common mineral found in many geologic environments. It is found in many intrusive igneous rocks ranging in composition from granites to diorite to gabbros to syenites. It occurs as phenocrysts in several varieties of extrusive igneous rocks, such an andesite.
Where is hornblende found?
