Name/Title
EpidositeEntry/Object ID
78.63.29Description
Chemical Composition: Ca2(Al,Fe)3(SiO4)3(OH)
Crystal System: Monoclinic System
Description: Common Name:Epidosite
Group Name:Silicates
Chemistry: Ca2(Al,Fe)3(SiO4)3(OH)
Location: Minas Genais,Brazil
Description: An olive and dark green Tourmaline crystal included within vein Quartz. Slender Tourmaline crystals scattered randomly throughout a massive Quartz crystal. Purplish Mica presents Lepidolite (Lithium Mica) and is characteristic of Tourmaline vein doposits. Piece is from Minas Genais, Brazil. Slender Tourmaline crystals are mostly green and Quartz is grey.
Physical Characteristics:
Color is "pistachio" green to yellowish or brownish green, also brown to black.
• Luster is vitreous.
• Transparency crystals are transparent to translucent.
• Crystal System monoclinic; 2/m
• Crystal Habits include long, somewhat prismatic or tabular crystals with a typically dominant pinacoid that the crystal is often flattened against. The terminations are wedge shaped or tappered pyramids. Many clusters show grooved slender crystals or acicular sprays. Also massive, fiberous or granular.
• Cleavage good in one direction lengthwise.
• Fracture is uneven to conchoidal.
• Hardness is 6-7
• Specific Gravity is 3.3-3.5
• Streak white to gray
• Associated Minerals calcite, biotite, hornblende, actinolite, andradite garnet and other metamorphic minerals.
• Other Characteristics: striated to the depth of grooves in some crystals.
• Notable Occurances Untersulzbachtal, Austria; Italy; Baja, Mexico and many localities in the USA.
• Best Field Indicators only one direction of cleavage, crystal habit, color and hardness.
Fracture: Uneven to Conchoidal
Hardness: 6 Orthoclase
Luster: Vitreous
Occurrence: Epidosite is a highly altered epidote and quartz bearing rock. It is the result of slow hydrothermal fluid alteration or metasomatism of the basaltic sheeted dike complex and associated plagiogranites that occurs below the massive sulfide ore deposits which occur in ophiolites. Epidosites represent the zone of intense metal leaching below and lateral to the sulfide deposits which is the result of convection of heated ocean water through the fractured basalts of the sheeted dikes. In colour they are pale yellow or greenish yellow, and they are hard. They may occur in more than one way and are derived from several kinds of rock.
Some have been sandstones; others are limestones which have undergone contact-alteration; probably the majority, however, are local modifications of rocks which were primarily basic intrusions or lavas.
• The sedimentary epidosites occur with mica-schists, they often show the remains of clastic structures.
• The epidosites derived from limestones may contain a great variety of minerals such as calcite, augite, garnet, scapolite, etc.
• The third group of epidosites may form bands, veins, or irregular streaks and nodules in masses of epidiorite and hornblende-schist. In microscopic section they are often merely a granular mosaic of quartz and epidote with some iron oxides and chlorite, but in other cases they retain much of the structure of the original rock though there has been a complete replacement of the former minerals by new ones.
Rock Type: Metamorphic
Specific Gravity: 3.3-3.5
Streak: whiteCollection
Delmar Smith Mineral CollectionDimensions
Width
3-1/2 inDepth
4 inLength
3 inDimension Notes
Dimension taken at widest points
