Rock-forming minerals, Volume 1,Deel 1

Preface to First Edition In writing these volumes the primary aim has been to provide a work of reference useful to advanced students and research workers in the geological sciences. It is hoped, however, that it will also prove useful to workers in other sciences who require information about minerals or their synthetic equivalents. Each mineral has been treated in some detail, and it has thus been necessary to restrict the coverage to a selection of the more important minerals. The principle in this selection is implied in the title Rock-Forming Minerals, as, with a few exceptions, only those minerals are dealt with which, by their presence or absence, serve to determine or modify the name of a rock. Some may quarrel with the inclusion or omission of particular minerals; once committed, however, to the discussion of a mineral or mineral series the less common varieties have also been considered. Most of the information contained in this text is available in the various scientific journals. An attempt has been made to collect, summarize and group these contributions under mineral headings, and the source of information is given in the references at the end of each section. The bibliography is not historically or otherwise complete, but the omission of reference to work which has been encompassed by a later and broader study does not belittle the importance of earlier investigations; where many papers have been published on a given topic, only a limited number have been selected to illustrate the scope and results of the work they report. The collection of data and references should bring a saving of time and labour to the research worker embarking on a mineralogical study, but it is hoped also that the presentation of the results of study from many different aspects, and in particular their correlation, will further the understanding of the nature and properties of the minerals. Determinative properties are described and tabulated, but the intended function of this work is the understanding of minerals as well as their identification, and to this end, wherever possible, correlation has been attempted, optics with composition, composition with paragenesis, physical properties with structure, and so on. For each mineral the body of well-established data is summarized, but unsolved and partially solved problems are also mentioned. The rock-forming minerals are dealt with in five volumes. The silicates are allocated on a structural basis: vol. 1. Ortho- and Ring Silicates, vol. 2. Chain Silicates, vol. 3. Sheet Silicates, vol. 4. Framework Silicates. Non-silicates are grouped chemically in the various sections of volume 5. With a few exceptions, the treatment of each mineral or mineral group is in five sub-sections. In the Structure section, in addition to a brief description of the atomic structure, descriptions of X-ray methods for determining chemical composition and any other applications of X-rays to the study of the mineral are given. The Chemistry section describes the principal variations in chemical composition and includes a table of analyses representative, wherever possible, of the range of chemical and paragenetic variation. From most analyses a structural formula has been calculated. The chemistry sections also consider the synthesis and breakdown of the minerals and the phase equilibria in relevant chemical systems, together with DT A observations and alteration products. The third section lists Optical and Physical Properties and discusses them in relation to structure and chemistry. The fourth section contains Distinguishing Features or tests by which each mineral may be recognized and in particular distinguished from those with which it is most likely to be confused. The Paragenesis section gives the principal

rock types in which the mineral occurs and some typical mineral assemblages: possible derivations of the minerals are discussed and are related wherever possible to the results of phase equilibria studies. The five sub-sections for each mineral are preceded by a condensed table of properties together with an orientation sketch for biaxial minerals and an introductory paragraph, and are followed by a list of references to the literature. The references are comprehensive to 1959 but later additions extend the coverage for some sections to 1961. In the present text, mineral data are frequently presented in diagrams, and those which can be used determinatively have been drawn to an exact centimetre scale, thus enabling the reader to use them by direct measurement: numbers on such diagrams refer to the number of the analysis of the particular mineral as quoted in the tables. The dependence of these volumes upon the researches and reports of very many workers will be so obvious to the reader as to need no emphasis, but we wish especially to record our indebtedness to those authors whose diagrams have served as a basis for the illustrations and thus facilitated our task. In this connection we would thank also the many publishers who have given permission to use their diagrams, and Mr H.C. Waddams, the artist who has so ably executed the versions used in the present text. Mineralogical Abstracts have been an indispensable starting point for bringing many papers to our attention: in by far the majority of cases reference has been made directly to the original papers; where this has not been possible the Mineralogical Abstracts reference is also given e.g. (M.A. 13-351). Our warmest thanks are due also to our colleagues in the Department of Geology, Manchester University, who have been helpful with discussions and information, and who have tolerated, together with the publishers, repeatedly over-optimistic reports about the work's progress and completion. We wish to thank Miss J.1. Norcott who has executed so efficiently the preparation of the typescript and also Longmans, Green & Co. for their continued cooperation. Department o/Geology, The University, Manchester 13.

October 1961

Preface to Second Edition For this completely new edition of Rock-Forming Minerals we have maintained the general principles and organization adopted for the first edition. The past twenty years, however, have seen an enormous expansion in activity in the Earth Sciences as a whole, and the subjects of Mineralogy and Petrology have certainly not been exceptions. The terms 'literature explosion' and 'exponential growth', although almost cliches, nevertheless are very apt in the present context. Not only have the numbers of researchers and their outputs increased, but exceptional growth has occurred in three particular fields: electron microprobe analysis, experimental petrology, and the determination of crystal structures. The facility of rapid and accurate electron probe analysis has replaced to a great extent the more laborious chemical and optical analytical methods, giving many more reliable analyses for each mineral and enabling researchers to examine more specimens and to complete a wider range of studies in a shorter time. The availability of more well-analysed material has also led to much more significant discussion of chemical variations and their relationships with crystal structure, physical properties and, most of all, parageneses. The important phenomena of fine-scale intergrowths (exsolution, etc.) and of chemical zoning have also been much more readily investigated using electron probe and other electron-optical methods. The study of phase equilibria at elevated pressures and temperatures has continued apace, so that the cumulative number of systems which need to be described has grown. In addition, much wider ranges of pressure and temperature have become accessible with improved techniques. At the same time, there has been a growth in the determination of thermodynamic properties of minerals, and in the experimental and theoretical approaches to element distribution within and between minerals. The advent and growing use of automatic single-crystal diffractometers has made it possible to determine crystal structures much more quickly, so that whereas there was hitherto perhaps one published structure for a mineral or even for a mineral group, now there can be structure determinations for a mineral at each of several chemical compositions, and at a number of different temperatures. The above, and other growth areas in mineralogy, have led to the fact that in this new edition the average number of pages devoted to each mineral is about three times that for the first edition. The extent of growth is indicated also by the list of references for each mineral which for this volume we have attempted to bring up to date to 1979, and the early months of 1981.

W. A. Deer

R. A. Howie

J. Zussman

April, 1982

Olivine Group

Olivine (Mg, Feh[Si0 4] Tephroite Mn2[Si04] Knebelite (Mn, Feh[Si0 4] Monticellite Ca(Mg, Fe)[Si0 4]

2

Orthosilicates

Olivine Group: Introduction The olivine group includes a number of closely related silicates which crystallize with orthorhombic symmetry. The structures of all the minerals of the group consist of independent SiO.. tetrahedra linked by divalent atoms in sixfold coordination. As is common in other orthosilicate minerals, silicon is not replaced by aluminium, and the octahedral positions in the structures are occupied almost exclusively by divalent ions; the common trivalent ions Al and Fe H are either absent, or present in very small amounts. In the (Mg,Fe)-olivines there is a continuous series between the two end-members Mg 2 Si0 4 (forsterite) and Fe 2 Si0 4 (fayalite): the fayalite - knebelite (FeMnSi0 4 ) - tephroite (Mn 2 Si0 4 ) series also shows complete solid solution. In the forsterite - fayalite series, however, manganese is usually present only in small amounts, and the low content of manganese in this series is probably related to the small amounts of manganese in the magmas and rocks in which they crystallized. A few occurrences of magnesium-rich tephroite, picrotephroite, have been reported. The CaMgSi0 4 orthosilicate (monticellite) does not vary greatly from the ideal composition, and members of the forsterite - fayalite series in general do not contain appreciable amounts of calcium. The iron analogue of monticellite, kirschsteinite (CaFeSi0 4 ) is known from slags, but has not been reported from a natural occurrence, and a magnesium-rich kirschsteinite containing 69 per cent CaFeSi0 4 is the most ironrich mineral of the Fe 2 Si0 4 - CaFeSi0 4 series yet reported. Glaucochroite (CaMnSi0 4) is a rare olivine, and minerals intermediate in composition between CaMgSi0 4 and CaMnSi0 4 are unknown. Common members of the olivine group, as well as NhSi0 4 , C0 2Si0 4 , and their germanate analogues have been synthesized. At high pressures and temperatures olivine is transformed to the y phase with a spinel structure, and at still higher pressures and temperatures to MgO + MgSi0 3 (rock salt and ilmenite t structures respectively). The minerals of the olivine group are very susceptible to alteration by hydrothermal and weathering processes and are often pseudomorphously replaced by minerals of low temperature paragenesis. The (Mg,Fe)-olivines are common and important rock-forming minerals, and are particularly characteristic of the ultrabasic and basic igneous rocks; often their composition is a useful indication of the differentiation stage of the parent magmas in which they crystallized. Monticellite is not a common mineral but occurs in some ultrabasic rocks and in metamorphosed and metasomatized limestone contacts with basic and acid intrusions. The other olivine minerals are rare and have a restricted paragenesis.

t

The perovskite structure may also be adopted at higher pressures.

Olivine (Mg,Feh[Si0 41 Orthorhombic (+) (-)

a· (J y

d

2Vy a = y, (J

= z,

Dispersion: D H Cleavage:

1'635 1'651 1'670 0'035 82 0 y=

x, O.A.P. (001)

r> v 3'222 7

1'827 1'869 1'879 0'052 134 0 a = y, (J = z, y = x, O.A.P. (001) r >v (over a) 4'392 6Y2 {010} moderate, {100} weak.

{010}, {lOO} imperfect. Twi~ning: {OIl}, {012}, {031} Green, lemon-yellow; colourless Pale yellow, greenish yellow, Colour: in thin section. yellow-amber; pale yellow in thin section. a = y pale yellow. Pleochroism: (J orange yellow, reddish brown. Unit cell.t a 4'8211 A a4'7540A b 10'1971 A b 10'4779A c 5'9806 A c6'0889A Z=4 Space group Pbnm.

Gelatinizes in HCl

• Values of refractive indices, birefringence and 2V refer to end-members, between which there is continuous variation. t Values for synthetic forsterite and fayalite (Schwab and Kustner, 1977).

4

Orthosilicates

The magnesium-rich olivines are common constituents of ultrabasic and ultramafic rocks. More iron-rich members occur in gabbros and ferrodiorites and fayalite is present in some acid and alkaline plutonic and volcanic rocks, as well as in the more highly differentiated ferrodiorites. Magnesium-rich olivines also occur in thermally metamorphosed impure dolomitic limestones, e.g. forsterite marble. The more iron-rich varieties occur as the products of regional metamorphism in eulysites and other metamorphosed iron-rich sediments. Magnesian olivine is generally considered to be the major constituent of the Earth's upper mantle, and the various physical properties and high pressure polymorphs, fJand y olivine, have been extensively studied particularly in relation to understanding the processes of deformation and the physical environment of this part of the mantle, and the various physical properties and high pressure polymorphs, f3diadochy, the (Mg,Fe)-olivines only rarely contain more than 4 wt. per cent MnO. Olivine is very susceptible to alteration, the products of which include various polymorphs of serpentine, talc, chlorite, iron oxides and carbonates. At high pressures, olivine is transformed to a solid solution (Mg,Fe) series with spinel structure, natural occurrences of which are restricted to shock-produced phases in chondri tic meteorites. The Mg-olivine, forsterite, is named after A. J. Forster, founder of the mineral collection known as the Heuland Cabinet, and the Fe-olivine, fayalite, after Faial Island in the Azores where it was believed to have occurred in a local volcanic rock, but it was probably obtained from slag carried as ship's ballast (Palache, 1950). The names forsterite and fayalite are restricted to the compositions Fo I 00 - 90 and Fo I 0 - 0 respectively; the nomenclature of the intermediate members of the series is given in Fig. 133 (p. 184). The clear gem-quality olivine is known as peridot.

Structure The structure of olivine was determined by Bragg and Brown (1926) for a crystal with composition F0 90 Falo with cell dimensions a 4'755 A, b 10'21 A, c 5'985 A. The structure consists of individual silicon-oxygen tetrahedra linked by magnesium atoms each of which has six nearest oxygen neighbours. The oxygens lie in sheets nearly parallel to the (100) plane and are arranged in approximate hexagonal close-packing. In accordance with full orthorhombic symmetry the silicon-oxygen tetrahedra point alternately either way along both x and y directions. Half of the available octahedral voids are occupied by M atoms (Mg,Fe) and one-eighth of the available tetrahedral voids by Si atoms. The magnesium atoms do not occupy a single set of equivalent lattice positions: half are located at centres of symmetry, I symmetry, and half on reflection planes, m symmetry (Fig. 1). Each oxygen is bonded to one silicon and three octahedrally coordinated atoms. The structure has subsequently been refined by a number of workers including Belov et al. (1951), Hanke and Zeman (1963), Hanke (1965), Birle et al. (1968), Kuroda (1969), and Wenk and Raymond (1973). Birle et al. (1968) drew attention to the relation between occupied and unoccupied octahedral sites within anyone (100) layer, the occupied octahedra forming a serrated chain as shown in Fig. 205, p. 384. The serrated chain in the next layer is related to that in the first by the b glide plane. The above feature of the structure is consistent with the observed {IOO} and {010} cleavages and the dominant {hkO} forms.

Olivine Group: Olivine

5

~----------b----------~

o

o

Fig. 1 Idealized olivine structure parallel to (100) pllne. Slatoms arc at the centres of tbe tetrahedra snd are not shown. Small open circle; Mg atoms at x = zero. Small solid circles; Mg atoms at x

=

Vl

(Ifter Brau_ad BrowD, 1916).

In detail the structure shows significant deviations from ideal hexagonal c1osepacking and both the octahedral and tetrahedral coordination polyhedra depart from their regular forms (Fig, 2), The Si-O bond lengths have three distinct values (Birle et ai" 1968); apical, Si-O(l) 1'614 and 1'619A, basal, Si-0(2) 1'654 and 1'657 A and Si-0(3,3') 1'635 and 1'637 A for forsterite and fayalite respectively, These values are in close accord with Si-O(l) = 1'617, Si-0(2) = 1'658 and Si- 0(3,3') = 1'635 A predicted for the SiO, tetrahedron by semiempirical molecular orbital calculations (Louisnathan and Gibbs, 1972), The MI polyhedron approximates to an octahedron flattened along a threefold axis, The mean M-O distance is larger for the M2 site, for forsterite M2-0 = 2' 135'&', MI-O =2' 103'&', and the M2 polyhedron is less regular and does not approximate to any simple distortion model.

OUvloe strudure PII ..... 10 (100) pllae .bowlng relatlolllhip of (a) Ideal hexaloaaJ cJosepacklol model, (b) actual slrudure (after HauD, 1976).

Fig. 1

6

Orthosilicates 4.80 a(A)

10.30

4.75

10.25

6.05 c(A)

b(.A)

10.20

6.00

A

10

20

30

40

50

(Fe.Mn.Cr.Ni) mole per cent Fig. 3 Lattice constants and mean interatomic distances Ml- 0 and Ml- 0 as a function of 1: Fe content, based on tbe data of Birle,t al. (1968), Finger (1971) and Wenk and Raymond (1973).

The mean MI-0 and M2-0 distances both increase linearly with increasing contents of the fayalite component (Fig. 3). The differences in the interatomic distances between MI-0 and M2-0 are small, some 0'035 A for forsterite and slightly less for compositions intermediate between forsterite and fayalite. The variations of the volumes of the Ml and M2 coordination polyhedra with Fecontent have been calculated by Wenk and Raymond (1973). The valence-bond distributions for these olivines, as well as those investigated by Birle et al. (1968), have been evaluated by Ferguson (1974) using a cationanion distance-dependent method. Assuming conventional tetrahedral and octahedral coordination for Si and (Mg,Fe) respectively, the results show that each of the three oxygen anions receive within 00'01 valence units (Le. within 00'5 per cent) of the ideal 2 v. u. (see also Born, 1964; Kuroda and Iguchi, 1971; Tossell, 1973). The orbital energy of the Si - 0 bonds in olivine, derived experimentally from X-ray photoelectron and emission spectra, has been shown to be considerably weaker than in quartz, and this appears to be due to second-nearest-neighbour differences rather than differences in bond length (Tossell, 1977). Structural variations in Mg - Fe olivines as a function of temperature have been studied by Brown and Prewitt (1973) and Smyth and Hazen (1973). The former, using two lunar olivines (F069 and F0 82 ) and a metamorphic olivine (grade corresponding with the sillimanite- muscovite zone, 650°C; 6 kbar), showed that the mean M1- 0, M2- 0 bond lengths, as well as the octahedral site volumes, increase (M1 site 1'81 per cent; M2 site 1-94 per cent) with increasing content of the fayalite component. Both M1-0 and M2-0 bond lengths increase at about the same rate (00-8 per cent) over the temperature range 24-710°C. The octahedral

Olivine Group: Olivine

7

site distortion was also found to increase with temperature indicating an increasing departure of the oxygen anions from ideal hexagonal close-packing. Smyth and Hazen's study on synthetic forsterite and a metamorphic (sillimanite grade) hortonolite, Mgo.7sFel.loMnoolsSi04, demonstrated that the forsterite unit cell parameters, a, band c (Table 1), and the cell volume expand by 0·81, 1·45, 1·33 and 3·63 per cent (the comparable values for the hortonolite are 0·83, 1·01, 1·33 and 3·05 per cent) between 20 and 900°C. Both studies showed that the Si-O interatomic distances remain practically constant in the temperature range of their investigations. Table 1.

CeU parameters of forsterite and fayaBte

Composition a(A) Fo 1oo Fo 1oo Fo 1oo Fo 1oo Fo 1oo Fo 1oo Fo 1oo Fo 1oo F0 96 Faloo Faloo Faloo Faloo Faloo At At c At d At - At f At a

b

4·76 4·756 4·756 4·758 4·816 4·752 4·797 4·7540 4·812 4·817 4·83 4·818 4·801 4·821 1

Reference 10·20 10·225 10·195 10·214 10·382 10·193 10·35 10·1971 10·565 10·477 10·49 10·470 10·22 10·4779

5·99 5·982 5·981 5·984 6·077 5·977 6·058 5·9806 6·085 6·105 6·10 6·086 6·049 6·0889

Swanson and Tatge, 1953 Eliseev, 1957 Yoder and Saharna, 1957 Skinner, 1962" Skinner, 1962 b Hazen, 1976c Hazen, 1976 d Schwab and Kustner, 1977 Eliseev, 1957 Yoder and Sahama, 1957 Hanke, 1963 Hazen, 1977Hazen, 1977' Schwab and Kustner, 1977

25°C. 1127 °C. 23°C.

1020 0c. 1 atm.

42 kbar.

The work of Smyth and Hazen (1973) on the thermal expansion of the unit-cell dimensions and cell volume has been extended to temperatures between -196 and 1020°C (Hazen, 1976), and his data are illustrated in the linear and volume expansion curves shown in Fig. 4a, b, and the Mg-O and Si-O mean bond lengths in Fig. 5. Hazen also determined the change in lattice parameters, MI-0 and M2-0 bond distances and polyhedral volumes of forsterite at pressures of 20,40 and 50 kbar. At the latter pressure the decrease in volume is .0 0·7 and 0·5 A3 in Ml and M2 sites respectively, and the total compression:o 10 A3 per unit cell. As there are four Ml and four M2 octahedra in the unit cell, 50 per cent of the compression in forsterite is thus probably due to contraction of the octahedral sites and 50 per cent to the contraction of voids. In a subsequent investigation, Hazen (1977) studied the variations in the crystal structure of a number of ferromagnesian olivines with temperature, pressure and Fe : Mg ratio. As in forsterite, expansion and compression of the octahedral sites occur with increasing temperature and pressure respectively, but the Fe : Mg ratio appears to have little effect on the bulk and linear thermal expansivities since the cell edges and volumes display approximately parallel expansion curves in the temperature range -196 to l000°C. At NTP the unit cell volume V = 290 + 17 xFeA 3, where X Fe is the octahedral Fe mole fraction. The effect of temperature on the unit cell volume, calculated from the experimental data, is approximately: AV = O·OO6T + 0·000006 T2 A3

8

Orthosilicates

:::1

304 302

4.76~ Q

/ ]

300

4.74

1O'401~1

298 (Al)

b

(A) 10.32

296

10.24 10.16

294

l:~I~J 200

1000

600

292 290 288 200

1400

Temperature (OK)

600

1000

1400

Temperature (0 K)

(a)

(b)

Fig. 4 (a) Forsterite unit cell dimensions versus temperature. (b) Forsterite unit cell volume versus temperature (after Hazen, 1976).

2.16

2.14

...--.

2.10

.-----

./

.~

1.641....----....

:::~

/

.~-o

·~...

-

!

,

,,1

.

.. " h _ _ I

~~-_