carbonate - calcite group Flashcards
calcite chemical formula
CaCO3
crystal form of calcite
- Hexagonal
- Three important habits: prismatic, rhombohedral, scalenohedral
- usually in crystals or in coarse- to fine-grained aggregates
- compact, earthy (as in chalk), and stalactitic (as in cave deposits).
calcite cleavage
rhombohedral perfect 74*55’
calcite hardness
3
calcite specific gravity
2.71
calcite color
- Usually white to colorless. Transparent to translucent
- Iceland spar is a chemically pure and optically colorless variety of calcite
- may be variously tinted gray, red, green, blue, yellow
- when impure, brown to black
- Luster vitreous to earthy
Calcite occurence
- one of the most common rock forming minerals
- igneous: a primary mineral or carbonatites and nepheline syenite; late crystallization product in the cavities in lava; in hydrothermal veins associated with sulfide ores
- meta: main constituent in marble
- sedimentary: main constituent in limestone; as stalagmites, stalactites, incrustations; travertine/tufa (cold/hot calcareous springs)
how to differentiate calcite from dolomite and aragonite
from dolomite: coarse calcite freely effervesces in cold dilute HCl
from aragonite: lower specific gravity and rhombohedral cleavage
magnesite formula
MgCO3
magnesite crystal form
- Rarely in rhombohedral crystals
- Usually cryptocrystalline in white, compact, earthy masses
- also in cleavable granular masses, coarse to fine.
magnesite cleavage
rhombohedral perfect
magnesite hardness
3.5 to 5
magnesite specific gravity
3 to 3.2
magnesite color
- Luster vitreous. Transparent to translucent.
- white gray yellow brown
magnesite occurence
- Common in veins and irregular masses derived from the alteration of Mg-rich metamorphic and igneous rocks; as such, a constituent of serpentinites and altered peridotites
= Such magnesite is compact and cryptocrystalline and may be associated with opaline silica. - Cleavable magnesite is found in talc, chlorite, and mica schists and in dolomitic limestones.
how to distinguish magnesite from chert and dolomite?
from chert: massive variety is softer than chert
from dolomite: has higher specific gravity
almost nonreactive to cold hcl, effervesces and dissolves with hot hcl