31:
183:
216:
To use this classification method, the concentrations (the modes) of the four mineral groups must be determined or estimated, and then normalized to 100%. Thus, for a rock identified as having, say, 20% mica, 30% quartz (Q), 30% alkali feldspar (A), and 20% plagioclase (P), the mica is disregarded,
240:
This diagram makes no distinction between rock types at the same QAPF plot position and classification, but of different bulk chemical compositions with respect to other minerals such as olivine, pyroxenes, amphiboles or micas. For example, because non-Q, -A, -P and -F minerals are disregarded the
229:
Of these, the (again) normalised relative proportions of A and P are 37.5/62.5 = 60% and 25/62.5 = 40%. The rock can now be plotted on the diagram by finding a horizontal line representing 37.5% quartz and then plotting a point on it 60% of the way across from the A side to the P side. For this
429:
Streckeisen, A. L., 1978. IUGS Subcommission on the
Systematics of Igneous Rocks. Classification and Nomenclature of Volcanic Rocks, Lamprophyres, Carbonatites and Melilite Rocks. Recommendations and Suggestions. Neues Jahrbuch für Mineralogie, Abhandlungen, Vol. 141,
213:, i.e., QAP and FAP. These are joined along one side such that, between them, each of the two triangle plots exclude either the Q group or F group minerals. (Other mineral groups may occur in samples, but they are disregarded in this classification method.)
433:
Le Maitre, R.W. 2002. Igneous Rocks: A Classification and
Glossary of Terms : Recommendations of International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Cambridge University Press,
209:
Because F and Q groups cannot simultaneously form in plutonic rocks—due to the difference in their respective silica contents—the QAPF diagram is drawn as two mutually exclusive
84:
groups used for classification in a QAPF diagram. The percentages (ratios) of the Q, A, P and F groups are normalized, i.e., recalculated so that their sum is 100%.
93:
280:(July 1974). "Classification and nomenclature of plutonic rocks recommendations of the IUGS subcommission on the systematics of Igneous Rocks".
104:(whence their alternative name: Streckeisen diagrams). Geologists worldwide use the diagrams in classifying igneous, especially plutonic rocks.
233:
And, a plutonic rock that contains no feldspathoids (F group), no alkali feldspar (A group), but contains plagioclase-feldspar (P group), many
410:
237:(not labeled in a QAPF diagram), and few quartz grains (Q group)—is probably gabbro; (see right edge of the Streckeisen diagram, at side P).
445:
174:
An exact name can be given only if the mineralogical composition is established, which cannot be determined in the field.
190:
The QAPF diagram presents for use the proportions (ratios) of four plutonic mineral(s) or mineral groups, which are:
129:
468:
217:
and the normalized ratios (proportions) of the Q, A, and P groups are calculated as 37.5%, 37.5% and 25% = 100%.
223:
i.e., (30 + 30 + 20= 80; then 30/80= 37.5%, 30/80= 37.5%, and 20/80= 25%; therefore 37.5 + 37.5 + 25= 100%).
473:
340:
260:
are the most important of groups that have separate classification diagrams; (see
Streckeisen diagram).
332:
289:
345:
148:(Total-Alkali-Silica) is used. TAS is also used if volcanic rock contains volcanic glass (such as
478:
358:
305:
277:
145:
101:
171:). Instead, an alternate triangle plot diagram is used; (see Streckeisen diagram, lower right.)
406:
350:
297:
137:
257:
195:
30:
451:
336:
293:
376:
462:
309:
121:
362:
323:
Le Bas, M. J.; Streckeisen, A. L. (1991). "The IUGS systematics of igneous rocks".
210:
203:
77:
53:
43:
17:
250:
199:
73:
168:
164:
117:
57:
354:
234:
125:
113:
182:
149:
69:
50:
301:
246:
158:
81:
61:
46:
242:
191:
65:
450:, Geological Sciences Department - Cal Poly Pomona, archived from
181:
155:
29:
405:(2nd ed.). Cambridge, UK: Cambridge University Press.
140:
or volcanic rocks if modal mineralogical compositions are
256:
The QAPF diagram is not used for all plutonic rocks; the
230:
447:
Classification of
Igneous Rocks - IUGS Classification
384:
British
Geological Survey: Rock Classification Scheme
98:Subcommission on the Systematics of Igneous Rocks
34:QAPF diagram for classification of plutonic rocks
403:Principles of igneous and metamorphic petrology
377:"Rock Classification Scheme - Vol 1 - Igneous"
161:make up more than 90% of the rock composition
8:
401:Philpotts, Anthony R.; Ague, Jay J. (2009).
132:have been determined. But QAPF diagrams are
112:QAPF diagrams are mostly used to classify
94:International Union of Geological Sciences
344:
269:
27:Classification system for igneous rocks
7:
241:system does not distinguish between
120:rocks), and can be used to classify
25:
325:Journal of the Geological Society
92:QAPF diagrams are created by the
130:modal mineralogical compositions
152:). QAPF diagrams are not used
1:
495:
258:ultramafic plutonic rocks
355:10.1144/gsjgs.148.5.0825
178:Reading the QAPF diagram
187:
80:", which are the four
35:
282:Geologische Rundschau
200:plagioclase feldspars
185:
44:doubled-triangle plot
33:
454:on 30 September 2011
337:1991JGSoc.148..825L
294:1974GeoRu..63..773S
278:Streckeisen, Albert
186:Streckeisen diagram
78:Feldspathoid (Foid)
18:QAPF classification
302:10.1007/bf01820841
188:
146:TAS classification
102:Albert Streckeisen
36:
469:Igneous petrology
412:978-0-521-88006-0
138:pyroclastic rocks
64:QAPF stands for "
49:used to classify
16:(Redirected from
486:
455:
417:
416:
398:
392:
391:
381:
373:
367:
366:
348:
320:
314:
313:
274:
196:Alkali feldspars
21:
494:
493:
489:
488:
487:
485:
484:
483:
459:
458:
444:
441:
426:
424:Further reading
421:
420:
413:
400:
399:
395:
379:
375:
374:
370:
346:10.1.1.692.4446
322:
321:
317:
276:
275:
271:
266:
180:
126:aphanitic rocks
110:
100:as fostered by
90:
70:Alkali feldspar
56:based on their
28:
23:
22:
15:
12:
11:
5:
492:
490:
482:
481:
476:
471:
461:
460:
457:
456:
440:
439:External links
437:
436:
435:
431:
425:
422:
419:
418:
411:
393:
368:
331:(5): 825–833.
315:
288:(2): 773–786.
268:
267:
265:
262:
227:
226:
225:
224:
211:triangle plots
179:
176:
163:(for example:
142:not determined
122:volcanic rocks
114:plutonic rocks
109:
106:
89:
86:
26:
24:
14:
13:
10:
9:
6:
4:
3:
2:
491:
480:
477:
475:
474:Igneous rocks
472:
470:
467:
466:
464:
453:
449:
448:
443:
442:
438:
432:
428:
427:
423:
414:
408:
404:
397:
394:
390:: 1–52. 1999.
389:
385:
378:
372:
369:
364:
360:
356:
352:
347:
342:
338:
334:
330:
326:
319:
316:
311:
307:
303:
299:
295:
291:
287:
283:
279:
273:
270:
263:
261:
259:
254:
252:
248:
244:
238:
236:
231:
222:
221:
220:
219:
218:
214:
212:
207:
205:
204:feldspathoids
202:(P), and the
201:
197:
193:
184:
177:
175:
172:
170:
166:
162:
160:
157:
151:
147:
143:
139:
135:
131:
127:
123:
119:
115:
107:
105:
103:
99:
95:
87:
85:
83:
79:
75:
71:
67:
63:
59:
55:
54:igneous rocks
52:
48:
45:
41:
32:
19:
452:the original
446:
402:
396:
387:
383:
371:
328:
324:
318:
285:
281:
272:
255:
239:
232:
228:
215:
208:
189:
173:
153:
144:. There the
141:
136:to classify
133:
111:
97:
91:
40:QAPF diagram
39:
37:
251:anorthosite
169:pyroxenites
165:peridotites
74:Plagioclase
463:Categories
264:References
118:phaneritic
58:mineralogy
479:Petrology
341:CiteSeerX
310:130569261
235:pyroxenes
198:(A), the
194:(Q), the
51:intrusive
363:28548230
159:minerals
150:obsidian
134:not used
96:(IUGS):
333:Bibcode
290:Bibcode
247:diorite
82:mineral
62:acronym
47:diagram
434:236pp.
409:
361:
343:
308:
249:, and
243:gabbro
192:quartz
88:Origin
66:Quartz
60:. The
430:1–14.
380:(PDF)
359:S2CID
306:S2CID
206:(F).
156:mafic
128:) if
108:Usage
42:is a
407:ISBN
167:and
351:doi
329:148
298:doi
154:if
465::
386:.
382:.
357:.
349:.
339:.
327:.
304:.
296:.
286:63
284:.
253:.
245:,
76:,
72:,
68:,
38:A
415:.
388:1
365:.
353::
335::
312:.
300::
292::
124:(
116:(
20:)
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
