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Correlation Course > Hermann-Mauguin Symmetry Symbols > Flashcards

Hermann-Mauguin Symmetry Symbols Flashcards

1
Q

Exhibits only the center of symmetry or no symmetry at all. Only 8% of minerals crystallize in this system.

A

Triclinic

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2
Q

No symmetry. No axes of rotation and no mirror planes. No center of symmetry. Faces on opposite sides are not equivalent.

A

Pedial (1)

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3
Q

A center of symmetry. Each face or point is matched on the opposite side by inversion through the center (i.e. opposite sides are equivalent). No axes of rotation and no mirror planes.

A

Pinacoidal (bar 1)

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4
Q

________ symbolizes “no symmetry”

A

1

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5
Q

1, 2, 3, 4, and 6 indicates an axis of _________.

A

rotational symmetry

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6
Q

The bar over show an axis of ______, usually called an _______.

A

rotation inversion; axis of inversion

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7
Q

The letter m, indicates a ______ usually referred to as a _______.

A

plane of symmetry; mirror plane

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8
Q

A slash “/” means ____________.

A

perpendicular to

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9
Q

The two-fold principle axis is uniquely the b-axis. The absence of a vertical mirror plane containing both the b-axis and c-axis makes recognition of this crystal system easy.

A

monoclinic crystal system

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10
Q

A single mirror plane perpendicular to the b-axis.

A

Domatic (m)

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11
Q

A 2-fold axis coincident with the b-axis. No mirror plane.

A

Sphenoidal (2)

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12
Q

A 2-fold axis (b-axis) perpendicular to a mirror plane. The mirror plane is visible when viewing the termination; if the crystal is in matrix the 2-fold axis may not be visible.

A

Prismatic (2/m)

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13
Q

It has 2/fold axis coincident with the c-axis. Two vertical mirror plane at 90 degrees angles to each other and containing 2 fold axis.

A

Orthorhombic crystal system

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14
Q

Two perpendicular mirror planes the intersection of which is a 2-fold c-axis. There is no horizontal mirror plane and the class is hemimorphic.

A

Orthorhombic pyramidal (mm2)

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15
Q

Three 2-fold axes mutually perpendicular and coincident with the crystallographic axes. No mirror planes.

A

Orthorhombic disphenoidal (222)

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16
Q

Three 2-fold axes each perpendicular to a mirror plane. Each 2-fold axis is coincident with a crystallographic axis.

A

Orthorhombic dipyramidal (2/m 2/m 2/m)

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17
Q

The unique feature is a single 3-fold or 3-fold inversion axis.

A

Trigonal crystal system

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18
Q

A 3-fold axis of rotation coincident with the c-axis. No mirror planes. Hemimorphic.

A

Trigonal pyramidal (3)

19
Q

A 3-fold axis of rotatory inversion coincident with the c-axis. No mirror planes.

A

Rhombohedral (bar 3)

20
Q

A 3-fold axis coincident with the c-axis and 3 vertical mirror planes each containing the c-axis and one a-axis. Hemimorphic.

A

Ditrigonal pyramidal (3m)

21
Q

A 3-fold axis coincident with the c-axis and perpendicular to a 3 2-fold axes. Each 2-fold axis is coincident with an a-axis.

A

Trigonal trapezohedral (32)

22
Q

A 3-fold axis of rotatory inversion perpendicular to 3 2-fold axes. Each 2-fold axis is coincident with an a-axis and perpendicular to a mirror plane. Holohedral.

A

Hexagonal scalenohedral (bar 3 2/m)

23
Q

The unique feature of this system is a 6-fold axis of rotation or a 6-fold inversion axis.

A

Hexagonal Crystal System

24
Q

A 6-fold inversion axis is equivalent to a 3-fold axis perpendicular to a mirror plane. No minerals have been found as a crystal.

A

Trigonal dipyramidal (bar 6 = 3/m)

25
Q

A 6-fold axis of rotation coincident with the c-axis. Hemimorphic.

A

Hexagonal pyramidal (6)

26
Q

A 6-fold axis of rotation coincident with the c-axis and perpendicular to a mirror plane.

A

Hexagonal dipyramidal (6/m)

27
Q

A 6-fold inversion axis coincident with the c-axis and centered in 3 vertical mirror planes each containing an a-axis; 3 2-fold axes coincident with the a-axes. Equivalent to a 3-fold axis perpendicular to a mirror plane and central to 3 vertical mirror planes each containing an a-axis.

A

Ditrigonal dipyramidal (bar 6m2 = 3/m m)

28
Q

A 6-fold axis coincident with and central to 6 vertical mirror planes; 3 coincident with the a-axes and 3 spaced evenly between the a-axes. Hemimorphic.

A

Dihexagonal pyramidal (6mm)

29
Q

A 6-fold axis coincident with the c-axis and perpendicular to 6 2-fold axes; 3 coincident with the a-axes and 3 spaced evenly between the a-axes. Enantiomorphic.

A

Hexagonal Trapezohedral (622)

30
Q

6-fold axis coincident with the c-axis and perpendicular ro 6 2-fold axes; 3 coincident with the a-axes and 3 spaced evenly between the a-axes; each axis perpendicular to a mirror plane. Holohedral.

A

Dihexagonal dipyramidal (6/m 2/m 2/m)

31
Q

A single 4-fold axis of rotational symmetry or rotatory inversion is the unique feature of this crystal system.

A

Tetragonal System

32
Q

A 4-fold rotatory inversion axis coincident with the c-axis.

A

Tetragonal disphenoidal (bar 4)

33
Q

A 4-fold axis coincident with the c-axis. Hemimorphic.

A

Tetragonal pyramidal (4)

34
Q

A 4-fold axis coincident with the c-axis perpendicular to a mirror plane.

A

Tetragonal dipyramidal (4/m)

35
Q

A 4-fold inversion axis coincident with the c-axis that is perpendicular to a 2 2-fold axes that are coincident with the a-axes. 2 vertical mirror planes containing the c-axis and intermediate to the a-axes.

A

Tetragonal scalenohedral (bar 42m)

36
Q

A fold axis parallel to and included in 4 vertical mirror planes. 2 mirror planes are coincident with the a-axis; the other two are intermediate to the a-xes.

A

Ditetragonal pyramidal (4mm)

37
Q

A 4-fold axis coincident with the c-axis and perpendicular to 4 2-fold axes; two of which are coincident with the a-axes and two of which are intermediate to the a-axes.

A

Tetragonal trapezohedral (422)

38
Q

A 4-fold axis coincident with the c-axis and perpendicular to a mirror plane. 2 2-fold axes perpendicular to 2 vertical mirror planes and coincident with the a-axes; and 2 2-fold axes intermediate to the a-axes and perpendicular to 2 vertical mirror planes.

A

Ditetragonal dipyramidal (4/m 2/m 2/m)

39
Q

The unique element of symmetry of this system is the presence of 4 3-fold axes. 7% of all known minerals.

A

Isometric (Cubic) System

40
Q

Three 2-fold axes coincident with the a-axes and four 3-fold diagonal axes.

A

Tetartoidal (23)

41
Q

Three 2-fold axes coincident with the a-axes and each perpendicular to a mirror plane; and four diagonal 3-fold inversion axes.

A

Diploidal (2/m bar 3)

42
Q

Three mutually perpendicular 4-fold inversion axes coincident with the a-axes; four axes of 3-fold symmetry; and six diagonal mirror planes.

A

Hextetrahedral (bar 43m)

43
Q

Three 4-fold axes coincident with the a-axes; four diagonal 3-fold axes; and six 2-fold axes.

A

Gyroidal (432)

44
Q

Three 4-fold axes perpendicular to mirror planes; 4 body-diagonal 3-fold inversion axes; 6 edge-diagonal 2-fold axes each perpendicular to a mirror plane.

A

Hexoctahedral (4/m bar 3 2/m)

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