Exploring How Pegmatites are Formed | Rock & Gem Magazine
2024年8月5日 · Pegmatite Pockets. We refer to the openings in a pegmatite as pockets because of their crystal content. They are also referred to as miarolitic cavities – a name taken from a pegmatite district in Italy. Miarolitic cavities only differ in their content from gem pegmatites in their chemistry and resulting crystal content – but all are ...
Pegmatite | Properties, Composition, Formation, Uses, Occurrence
2019年4月12日 · Pegmatites form from waters that separate from a magma in the late stages of crystallization; this activity often occurs in small pockets along the margins of a batholith. Pegmatite can also form in fractures that develop on the margins of the batholith.
Formation of tourmaline-rich gem pockets in miarolitic pegmatites
Whether gem pockets form may be dependent largely on the timing of tourmaline crystallization. Formation of tourmaline removes an alkali borate component from residual pegmatitic melt, with the consequent deposition of other alkali aluminosilicate and oxide-forming minerals and exsolution of copius amounts of H 2 O.
Pegmatite: Formation, Composition, Properties, Uses - Geology In
Crystallization pockets: Pegmatites often occur in pockets or veins within other rock formations, creating isolated environments conducive to the formation of giant crystals. Pegmatite Mineral Composition. While most pegmatites share a similar composition to granite, they can exhibit a wider range of mineral assemblages.
previous studies from gem pegmatites of San Diego County, California, indicate that pocket development in tourmaline-rich, miarolitic rare-element pegmatites occurs between ap- proximately 475 and, 425C and between 2800 and 2400 bars.
Pegmatite genesis: state of the art - GeoScienceWorld
2008年8月1日 · Based on stable isotopic studies, Taylor et al. proposed temperatures of emplacement of pegmatite melts at about 700 °C to final temperatures of 525 °C in the pockets in San Diego County, California pegmatites.
Conditions of pocket formation in the Oktyabrskaya tourmaline …
2004年10月27日 · The largest pockets (>0.5 m across) in the Malkhan pegmatites reveal decrepitation and fluid incursion into the fractures of the hosting quartz–feldspar pegmatite. The neighboring pockets are often interconnected via small channels and veinlets indicating an exchange of matter between them.
pockets. The elongate, ligh t-colored crystals are common spodumene reaching 5 m in length. Photo by Richard H. Jahns. pegmatites can exceed by several orders of magni- tude the amounts found in other rocks. In fact, the mining of pegmatites for rare elements, or even for the common pegmatite minerals, has at times
Petrogenesis of zoned and unzoned mafic pegmatites: An insight …
2022年11月1日 · The mafic-ultramafic Hamn intrusion hosts pockets of unzoned and zoned mafic pegmatites. Most of the unzoned pegmatite pockets are hosted in gabbronorite; however, the sample PH-HM-32 shows a sharp transition from a fine-grained host gabbro to …
Gem-Bearing Pegmatites: A Review | Gems & Gemology - GIA
Pegmatites are typically rather small bodies of rock that are found in particular geologic environments; the gem minerals occur in open cavities or "pockets" within the pegmatite. This article surveys our current understanding of pegmatites, beginning with a brief description of their characteristics and following with a discussion of the ...