Name/Title
Oligoclase / AugiteEntry/Object ID
2009.62.132Description
Chemical Composition: Sodium calcium aluminum
Crystal System: Triclinic System
Description: Common Name: Oligoclase / Augite
Chemistry: Na(90-70%) Ca(10-30%) (Al, Si)AlSi2 O8, Sodium calcium aluminum silicate. / (Ca, Na)(Mg, Fe, Al)(Al, Si)2 O6, Calcium Sodium Magnesium Iron Aluminum Silicate.
Group: Feldspars / Pyroxenes
Location: Mina de la Pili, Chihuahua, Mexico
Description: Small angular gray crystals with one pertruding black crystal as well as some smaller black crystals imbedded in the cluster.
PHYSICAL CHARACTERISTICS OF OLIGOCLASE:
Color is usually off-white or gray or pale shades of green, yellow or brown.
Luster is vitreous to dull if weathered..
Transparency crystals are translucent to transparent.
Crystal System is triclinic; bar 1
Crystal Habits include blocky, or tabular crystals. Crystals have a nearly rectangular or square cross-section with slightly slanted dome and pinacoid terminations. Twinning is almost universal in all plagioclases. Crystals can be twinned according to the Albite, Carlsbad, Manebach and Baveno laws. Oligoclase can be found as a major rock forming component in granites and syenites.
Cleavage is perfect in one and good in another direction forming nearly right angled prisms.
Fracture is conchoidal.
Hardness is 6 - 6.5.
Specific Gravity is approximately 2.64 - 2.68 (average)
Streak is white.
Associated Minerals are quartz, muscovite and K-feldspars.
Other Characteristics: index of refraction is 1.533 - 1.552. Lamellar twinning may cause a grooved effect on cystal and cleavage surfaces that appear as striations.
Best Field Indicators are occurrence, twinning striations, shimmer, density and index of refraction.
PHYSICAL CHARACTERISTICS OF AUGITE:
Color is dark green, brown and black
Luster is vitreous to submetallic and even dull.
Transparency crystals are transparent to mostly translucent or opaque.
Crystal System is monoclinic; 2/m
Crystal Habits include short prismatic, rarely tabular crystals. The square cross section is distinctive in the prismatic crystals. Also compact, granular, columnar, lamellar and fibrous(rare).
Cleavage is perfect in two lengthwise directions at close to right angles.
Fracture is uneven.
Hardness is 5 - 6
Specific Gravity is approximately 3.2 - 3.6 (slightly above average)
Streak is greenish white.
Other Characteristics: The basal parting is prominent.
Associated Minerals are olivine, biotite, nepheline, albite, apatite, serpentine, leucite and hornblende.
Best Field Indicators are crystal habit, associations, color, parting and cleavage.
Fracture: Conchoidal
Hardness: 6 Orthoclase
Luster: Vitreous
Occurrence: Oligoclase occurs, often accompanying orthoclase, as a constituent of plutonic igneous rocks such as granite, syenite, and diorite. It occurs in porphyry and diabase dikes and sills as well as in the volcanic rocks andesite and trachyte. It also occurs in gneiss
Rock Type: Sedimentary
Specific Gravity: 2.6
Streak: whiteCollection
RAGM Mineral CollectionAcquisition
Accession
2009.62Source or Donor
Museum Collection of MineralsAcquisition Method
DonationDimensions
Width
2-3/4 inDepth
1-1/4 inLength
2 inWeight
0.44 ozLocation
Location
Display Case
FS-6Room
Frieda Smith HallBuilding
Crater Rock MuseumDate
January 3, 2024Location
Container
CenterDrawer
Top ShelfShelf
Right, RightWall
West wallRoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Steve MillerDate
January 30, 2010Location
Drawer
3rd from leftShelf
top shelf right side, top shelf right sideWall
West wallRoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Scott LonganDate
September 26, 2009Location
Container
CenterDrawer
Top ShelfShelf
RightCabinet
Case# 30Wall
EastBuilding
Freida Smith HallCategory
Permanent
