Porphyritic texture

Texture and structure are not explicitly defined terms. Structure is usually applied to macroscopic heterogeneity due to macroscopic movement such as flow structure or foliated structure, whereas texture usually refers to microscopic heterogeneity, such as holocrystalline texture, porphyritic texture, and lamellar texture due to exsolution. 

Monte Amiata is a 1738 m-high cone dominated by trachydacitic lava flows and domes with a few late-erupted shoshonites and latites. Magmatism is 0.3 to 0.2 Ma and is associated with well-known and long-exploited cinnabar mineralisations (Mazzuoli and Pratesi 1963 Barberi et al. 1971 van Bergen 1985 Ferrari et al. 1996 and references therein). The Monte Amiata trachydacites exhibit a porphyritic texture with abundant... 

The largest intrusion is represented by the Monte Capanne monzogran-itic stock (about 10 km in diameter), located in the western side of the island. It exhibit a porphyritic texture with centimetre- to decimetre-sized euhedral megacrysts of K-feldspar that are set in a medium- to coarsegrained matrix formed by variable amounts of plagioclase, quartz, K-feldspar and biotite with accessory apatite, zircon, monazite, ilmenite, and tourmaline. The intrusion contains abundant microgranular calc-alkaline... 

Most lava flows exhibit poorly porphyritic textures. Main phenocryst phases include leucite and clinopyroxene olivine and Fe-Ti oxides occur in minor amounts. Groundmass contains the same phases plus nepheline,... 

The SiC>2 vs. K2O plot (Fig. 7.8) shows that the Lipari volcanics define a steep increase in K2O from mafic to intermediate rocks, straddling the limits between arc tholeiitic, calc-alkaline and shoshonitic series. Basaltic andesites and andesites have porphyritic textures with phenocrysts of zoned... 

Cornacya Seamount. This seamount recently was discovered, named and studied by Mascle et al. (2001). It is an about 12 Ma old volcano located SE of the southern Sardinian coast. Samples from Cornacya consist of strongly altered lavas that contain enclaves of mica-rich lamprophyres. The lavas have varied porphyritic textures with ubiquitous phenocrysts of zoned plagioclase and biotite plus some amphibole and clinopyroxene that are surrounded by a glass-rich matrix containing minor Na-rich plagioclase, anorthoclase, biotite and secondary products. Accessory minerals include Fe-Ti oxides, apatite and zircon. The lamprophyric enclaves are por-... 

Figure 1 Maps showing magnesium concentrations in two chondrites (a) PCA91082, a CR2 carbonaceous chondrite, and (b) Tieschitz, an H/L3.6 ordinary chondrite. In CR chondrites, as in most carbonaceous chondrites, nearly all chondrules have porphyritic textures and are composed largely of forsterite (white grains), enstatite (gray), and metallic Fe,Ni (black). The subscripts show type I chondrules, which are common, and type II, which are FeO-rich and rare in this chondrite. Tieschitz, like other ordinary chondrites, is composed of all kinds of chondrules with diverse FeO concentrations. Key to chondrule t3fpes BO, barred olivine C, cryptocrystalline, PO, porphyritic olivine POP, porphyritic olivine-pyroxene PP, porphyritic pyroxene RP, radial pyroxene. These maps were made with an electron microprobe from Mg Ka X-rays.

Oxygen-isotopic compositions of aluminum-rich chondrules from CR and CH chondrites (Krot et al, 2003c) are plotted in Figure 15(b). Three out of six chondrules analyzed exhibit large internal-isotopic heterogeneity, whereas others are iso-topically uniform all chondrules have porphyritic textures. In contrast to aluminum-rich chondrules in ordinary chondrites, oxygen isotopic heterogeneity is due to the presence of relict CAIs (Krot and Keil, 2002). 

W21d. 12.27.63) Rhyolite, grayish red with prominent red-brown flow banding. Porphyritic texture, highly embayed quartz, and pseudomorphs of seridte after feldspar with inclusions of altered pumice. Red-Brown Member, Bragg Valley, southern... 

K5 Locally shown as intrusion Compose of plagioclase, opaque minerals, chlorite and sericite, cement is clay and carbonate, semi-crystalline porphyritic texture, as a result of alteration, plagioclases were carbonated, sericited and chlorited. Diabase... 

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