6.58 Analcime from Martinique; image is 16 cm across6.59 Leucite from Brazil6.60 Nepheline6.61 Sodalite with calcite from AfghanistanThe photos above in Figures 6.58 to 6.61 show the most common feldspathoids. They have compositions that are, for the most part, equivalent to silica-deficient feldspars. These minerals commonly crystallize from magmas that are relatively low in SiO2 or that contain more Na, K, and Al than can fit into feldspars. These minerals have large openings in their atomic arrangements that allow the minerals to contain significant amounts of large anions and molecular anions, including chlorine, carbonate, and sulfate. They often occur with feldspars, and also with mafic minerals including amphiboles, olivine, and pyroxenes, but never with quartz. They are restricted to quartz-free rocks because they will react with quartz to produce feldspars by reactions such as:
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Analcime, a zeolite, is often considered to belong to the feldspathoid family. Other important feldspathoids include leucite, nepheline, sodalite, and lazurite. Leucite is a rare mineral found in K-rich volcanic rocks. It is unknown in plutonic, metamorphic, or sedimentary rocks. Nepheline is a common mineral in syenite and other silica-poor volcanic or plutonic igneous rocks. Leucite and nepheline are usually associated with K-feldspar. Sodalite crystallizes from alkali-rich magmas and is also found in some metamorphosed carbonate rocks. Analcime also can crystallize from a magma, but it more commonly forms as a secondary mineral in vugs, cracks, or veins. Occasionally it is found as a secondary mineral in sandstones or tuffs. When it crystallizes from a magma, it is typically associated with olivine, leucite, and perhaps sodalite. When it is secondary, other low-temperature minerals, including zeolites or prehnite, often accompany it.
Figure 6.88 shows glaucophane, a blue sodic amphibole, that has the general formula Na2Al2Si8O22(OH)2. Its presence is often associated with rocks formed in subduction zones under high pressures and moderate temperatures. Other Ca-free amphiboles (anthophyllite, gedrite, cummingtonite, and grunerite) are found in metamorphic rocks and occasionally in extrusive igneous rocks. Tremolite is common in high-temperature marbles. As with some other silicates found in marbles, identifying it may be difficult because of its inconspicuous white color. See Figure 6.85, above.
The journey up from the Midlands was straightforward, with no problems. We decided to park at the Sunderland Enterprise 'Park and Ride' where we saw a sign for 'Match Day Parking'. A steward signalled us to follow him and told us where to park. When we got out of our car, we asked two Sunderland fans how it worked as we wasn't sure if we had to pay. They told us that it was actually free, which was really good. They also showed us where to get the bus to the stadium and where to catch it after the match had ended. We chatted with them on the way and they seemed friendly enough.
I travelled up from where I live in Scunthorpe giving myself plenty of time. The trip was via the M181, M18, A1 and A19 and was hassle free on a lovely sunny day. The scenery as I progressed north was lovely, including some sea views. Journey time was 2 hours 10 minutes to cover the 140 miles. I parked in a spot made known to me by a fellow Scunthorpe Spur. I ended up parking, for free, on some waste land at the junction of Thomas Street and Alexandra Avenue. From the parking space it was a 10-15 minute walk to the ground. I cut through Wayfarer Road and then followed a footpath down by the river Wear. When near the ground, I climbed a grassy bank with a defined footpath already worn into it.
Sunderland have a fanzone at the stadium which was pretty decent. Both sets of fans mixed freely with no hint of trouble. Most Sunderland fans I met were really happy for Leicester and the position we are in. 2ff7e9595c
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