carbonate - calcite group Flashcards

1
Q

calcite chemical formula

A

CaCO3

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2
Q

crystal form of calcite

A
  • 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).
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3
Q

calcite cleavage

A

rhombohedral perfect 74*55’

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4
Q

calcite hardness

A

3

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5
Q

calcite specific gravity

A

2.71

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6
Q

calcite color

A
  • 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
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7
Q

Calcite occurence

A
  • 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)
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8
Q

how to differentiate calcite from dolomite and aragonite

A

from dolomite: coarse calcite freely effervesces in cold dilute HCl
from aragonite: lower specific gravity and rhombohedral cleavage

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9
Q

magnesite formula

A

MgCO3

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10
Q

magnesite crystal form

A
  • Rarely in rhombohedral crystals
  • Usually cryptocrystalline in white, compact, earthy masses
  • also in cleavable granular masses, coarse to fine.
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11
Q

magnesite cleavage

A

rhombohedral perfect

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12
Q

magnesite hardness

A

3.5 to 5

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13
Q

magnesite specific gravity

A

3 to 3.2

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14
Q

magnesite color

A
  • Luster vitreous. Transparent to translucent.
  • white gray yellow brown
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15
Q

magnesite occurence

A
  • 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.
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16
Q

how to distinguish magnesite from chert and dolomite?

A

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

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17
Q

siderite formula

A

FeCO3

18
Q

siderite crystal form

A
  • Commonly in rhombohedral crystals, which may show curved faces
  • in globular concretions and
  • cleavable masses
  • May be botryoidal, compact, and earthy.
19
Q

siderite cleavage

A

rhombohedral perfect

20
Q

siderite hardness

A

3.5 to 4

21
Q

siderite specific gravity

A

3.96 (pure)

22
Q

siderite color

A
  • Luster vitreous. Transparent to translucent.
  • light to dark brown
23
Q

siderite occurence

A
  • As a vein mineral, in well-crystallized form, it is associated with metallic ores containing silver minerals, pyrite, chalcopyrite, and galena.
  • It also occurs as clay ironstone, with admixed clay minerals, in concretions with concentric layers.
  • Also found in shales and coal measures as blackband ore, contaminated with carbonaceous material.
  • It is also a common constituent of sedimentary Precambrian iron-formations, in association with chert and magnetite.
24
Q

how to distinguish siderite from other carbonates? and specifically from sphalerite?

A

from other carbonates: brownish color and high specific gravity
from sphalerite: rhombohedral cleavage

in powder soluble by hot hcl, in fragments by hot hcl

25
Q

rhodocrosite formula

A

MnCO3

26
Q

rhodocrosite crystal form

A
  • rarely rhombohedral maybe with cruved faces
  • granular to compact
  • cleavable, massive
27
Q

rhodocrosite cleavage

A

rhombohedral perfect

28
Q

rhodocrosite hardness

A

3.5 to 4

29
Q

rhodocrosite specific gravity

A

3.5 to 3.7

30
Q

rhodocrosite color

A
  • shades of rose red, light pink to dark brown
  • vitreous, transparent to translucent
31
Q

rhodocrosite occurence

A
  • hydrothermal veins with ore minerals of silver, lead, copper and of manganese deposits
32
Q

how to distinguish rhodocrosite, specifically from rhodonite

A

in general: pink color and rhombohedral cleavage, soluble in hot HCl
from rhodonite: hardness of 4 vs rhodonite’s 6

33
Q

smithsonite formula

A

ZnCO3

34
Q

smithsonite crystal form

A
  • usually reniform, botryoidal, stalactitic
  • rarely in small rhomboheral or scalenohedral crystals
  • crystalline incrustations, granular to earthy
35
Q

smithsonite cleavage

A

rhombohedral perfect

36
Q

smithsonite hardness

A

4 to 4.5

37
Q

smithsonite specific gravity

A

4.3 to 4.45

38
Q

smithsonite color

A
  • vitreous, translucent to colorless, white
  • dirty brown, pink, green, blue
  • yellow variety is called turkey-fat ore
39
Q

smithsonite occurence

A

(is a zinc ore of supergene origin)
- in zinc deposits in limestone
- associated with limonite, cerussite, calcite, galena, sphalerite, hemimorphite

40
Q

smithsonite remarks

A
  • its reniform, botryoidal and stalactitic habit
  • powdered form reacts with hot HCl
  • distinguish from other carbonates with its 4 hardness and high specific gravity