page_title: Pegmatite
hierarchical_section_title: Pegmatite
caption_attribution_description: small glacier hanging in there on northeastern Baffin Island the swarm of pegmatite sills in the rock wall were injected during a prior mountain building episode or ancient continental collision way back in Proterozoic times link to a pegmatite sample in my photostream flic.kr/p/duL3Zq link to my ABC Geology gallery www.flickr.com/photos/31856336@N03/galleries/721576239751...
context_page_description: A pegmatite is an igneous rock, formed underground, with interlocking crystals usually larger than 2.5 cm in size. Most pegmatites are found in sheets of rock near large masses of igneous rocks called batholiths.
  The word pegmatite derives from Homeric Greek, πήγνυμι, which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite.
  Most pegmatites are composed of quartz, feldspar and mica, having a similar silicic composition as granite. Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene, feldspathoids and other unusual minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions.
  Crystal size is the most striking feature of pegmatites, with crystals usually over 5 cm in size. Individual crystals over 10 metres long have been found, and many of the world's largest crystals were found within pegmatites. These include spodumene, microcline, beryl, and tourmaline.
  Similarly, crystal texture and form within pegmatitic rock may be taken to extreme size and perfection.
context_section_description: A pegmatite is an igneous rock, formed underground, with interlocking crystals usually larger than 2.5 cm in size (1 in). Most pegmatites are found in sheets of rock (dikes and veins) near large masses of igneous rocks called batholiths.
  The word pegmatite derives from Homeric Greek, πήγνυμι (pegnymi), which means “to bind together”, in reference to the intertwined crystals of quartz and feldspar in the texture known as graphic granite. 
  Most pegmatites are composed of quartz, feldspar and mica, having a similar silicic composition as granite. Rarer intermediate composition and mafic pegmatites containing amphibole, Ca-plagioclase feldspar, pyroxene, feldspathoids and other unusual minerals are known, found in recrystallised zones and apophyses associated with large layered intrusions.
  Crystal size is the most striking feature of pegmatites, with crystals usually over 5 cm in size. Individual crystals over 10 metres (33 ft) long have been found, and many of the world's largest crystals were found within pegmatites. These include spodumene, microcline, beryl, and tourmaline.
  Similarly, crystal texture and form within pegmatitic rock may be taken to extreme size and perfection. Feldspar within a pegmatite may display exaggerated and perfect twinning, exsolution lamellae, and when affected by hydrous crystallization, macroscale graphic texture is known, with feldspar and quartz intergrown. Perthite feldspar within a pegmatite often shows gigantic perthitic texture visible to the naked eye. The product of pegmatite decomposition is euclase.
caption: Proterozoic pegmatite swarm in the headwall of the cirque of a small mountain glacier, northeastern Baffin Island, Nunavut.
exif: {"Image Make": "FUJIFILM", "Image Model": "FinePix J250", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Digital Camera FinePix J250 Ver1.00", "Image DateTime": "2012:07:22 12:27:09", "Image YCbCrPositioning": "Co-sited", "Image Copyright": "", "Image ExifOffset": "300", "Image PrintIM": "[80, 114, 105, 110, 116, 73, 77, 0, 48, 50, 53, 48, 0, 0, 2, 0, 2, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0]", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail Orientation": "Horizontal (normal)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "1386", "Thumbnail JPEGInterchangeFormatLength": "11174", "Thumbnail YCbCrPositioning": "Co-sited", "EXIF ExposureTime": "1/350", "EXIF FNumber": "26/5", "EXIF ExposureProgram": "Program Normal", "EXIF ISOSpeedRatings": "64", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2012:07:22 12:27:09", "EXIF DateTimeDigitized": "2012:07:22 12:27:09", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "4", "EXIF ShutterSpeedValue": "212/25", "EXIF ApertureValue": "47/10", "EXIF BrightnessValue": "5", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "17/5", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "51/10", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "3648", "EXIF ExifImageLength": "2736", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "1238", "EXIF FocalPlaneXResolution": "6129", "EXIF FocalPlaneYResolution": "6129", "EXIF FocalPlaneResolutionUnit": "3", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF SceneCaptureType": "Standard", "EXIF Sharpness": "Normal", "EXIF SubjectDistanceRange": "0"}