Rit (Vísindafélag Íslendinga) - 01.06.1967, Page 186

Rit (Vísindafélag Íslendinga) - 01.06.1967, Page 186
182 mass has a fluidal texture, plagioclase needles being the only discernible mineral and these needles are all oriented parallel to the flow. Conspicuous is a colour banding due to different content of glass in the groundmass, which results in diffe- rent shades of brown to nearly black (Fig. 1). The bands fol- low the direction of the flow. The fluidal texture curves around the phenocrysts, especially the pyroxenes. The amount of phenocrysts is usually less than 2%. The length of the plagioclase crystals is 2= 1.5 mm, of the pyroxenes ^ 1 mm, of the titanomagnetites 0.3—0.5 mm. The olivines are some- what smaller and there are some apatite crystals grouped near or within the pyroxene and titanomagnetite crystals. In the first phase of the 1845/46 lava — sample collected high up in the mountain slopes — we find the following re- fractive indices and composition of the phenocrysts: Plagioclase: nx 1.558, nz 1.566 An 60 Pyroxene: — 1.701, — 1.723 2V = 45° Olivine: - 1.730, - 1.779 Fa 50-53 In the first phase of the 1947 lava — sample collected from a lava tongue from the first day of eruption — we find the following indices and composition of phenocrysts: Plagioclase: nx 1.558, nz 1.564 An 57 Pyroxene: — 1.701, — 1723 Olivine: — 1.730, — 1.781 Fa 55 In spite of the absence of quartz the type I lava is classi- fied as dacite. The groundmass of the lava of the second phase (type II lava, Fig. 2) is considerably more coarse-grained than in the lavas of the first phase, but contains the same minerals as phenocrysts, although more of olivine and in bigger crystals. The content of phenocrysts varies a lot, from nearly nothing to about 3%. The titanomagnetites are most conspicuous in samples containing the smallest amount of apatite and often surrounded by the latter. The groundmass consists of plagio-
Page 1
Page 2
Page 3
Page 4
Page 5
Page 6
Page 7
Page 8
Page 9
Page 10
Page 11
Page 12
Page 13
Page 14
Page 15
Page 16
Page 17
Page 18
Page 19
Page 20
Page 21
Page 22
Page 23
Page 24
Page 25
Page 26
Page 27
Page 28
Page 29
Page 30
Page 31
Page 32
Page 33
Page 34
Page 35
Page 36
Page 37
Page 38
Page 39
Page 40
Page 41
Page 42
Page 43
Page 44
Page 45
Page 46
Page 47
Page 48
Page 49
Page 50
Page 51
Page 52
Page 53
Page 54
Page 55
Page 56
Page 57
Page 58
Page 59
Page 60
Page 61
Page 62
Page 63
Page 64
Page 65
Page 66
Page 67
Page 68
Page 69
Page 70
Page 71
Page 72
Page 73
Page 74
Page 75
Page 76
Page 77
Page 78
Page 79
Page 80
Page 81
Page 82
Page 83
Page 84
Page 85
Page 86
Page 87
Page 88
Page 89
Page 90
Page 91
Page 92
Page 93
Page 94
Page 95
Page 96
Page 97
Page 98
Page 99
Page 100
Page 101
Page 102
Page 103
Page 104
Page 105
Page 106
Page 107
Page 108
Page 109
Page 110
Page 111
Page 112
Page 113
Page 114
Page 115
Page 116
Page 117
Page 118
Page 119
Page 120
Page 121
Page 122
Page 123
Page 124
Page 125
Page 126
Page 127
Page 128
Page 129
Page 130
Page 131
Page 132
Page 133
Page 134
Page 135
Page 136
Page 137
Page 138
Page 139
Page 140
Page 141
Page 142
Page 143
Page 144
Page 145
Page 146
Page 147
Page 148
Page 149
Page 150
Page 151
Page 152
Page 153
Page 154
Page 155
Page 156
Page 157
Page 158
Page 159
Page 160
Page 161
Page 162
Page 163
Page 164
Page 165
Page 166
Page 167
Page 168
Page 169
Page 170
Page 171
Page 172
Page 173
Page 174
Page 175
Page 176
Page 177
Page 178
Page 179
Page 180
Page 181
Page 182
Page 183
Page 184
Page 185
Page 186
Page 187
Page 188
Page 189
Page 190
Page 191
Page 192
Page 193
Page 194
Page 195
Page 196
Page 197
Page 198
Page 199
Page 200
Page 201
Page 202
Page 203
Page 204
Page 205
Page 206
Page 207
Page 208
Page 209
Page 210
Page 211
Page 212
Page 213
Page 214
Page 215
Page 216
Page 217
Page 218

x

Rit (Vísindafélag Íslendinga)

Direct Links

If you want to link to this newspaper/magazine, please use these links:

Link to this newspaper/magazine: Rit (Vísindafélag Íslendinga)
https://timarit.is/publication/1735

Link to this issue:

Link to this page:

Link to this article:

Please do not link directly to images or PDFs on Timarit.is as such URLs may change without warning. Please use the URLs provided above for linking to the website.