Metamorphic Facies Defined and Explained

Metamorphic Facies Defined and Explained As metamorphic rocks change under heat and pressure, their ingredients recombine into new minerals that are suited to the conditions. The concept of metamorphic facies is a systematic way to look at the mineral assemblages in rocks and determine a potential range of pressure and temperature (P/T) conditions that were present when they formed.   It should be noted that metamorphic facies are different than sedimentary facies, which include the environmental conditions present during deposition. Sedimentary facies can be further divided into lithofacies, which focus on a rocks physical characteristics, and biofacies, which focus on the paleontological attributes (fossils).   Seven MetamorphicFacies There are seven widely recognized metamorphic facies, ranging from the zeolite facies at low P and T to eclogite at very high P and T. Geologists determine a facies in the lab after examining many specimens under the microscope and doing bulk chemistry analyses. Metamorphic facies is not obvious in a given field specimen. To sum up, a metamorphic facies is the set of minerals found in a rock of a given composition. That mineral suite is taken as a sign of the pressure and temperature that made it. Here are the typical minerals in rocks that are derived from sediments. That is, these will be found in slate, schist and gneiss. The minerals shown in parentheses are optional and dont always appear, but they can be essential for identifying a facies. Zeolite facies: illite/phengite chlorite quartz (kaolinite, paragonite)Prehnite-pumpellyite facies: phengite chlorite quartz (pyrophyllite, paragonite, alkali feldspar, stilpnomelane, lawsonite)Greenschist facies: muscovite chlorite quartz (biotite, alkali feldspar, chloritoid, paragonite, albite, spessartine)Amphibolite facies: muscovite biotite quartz (garnet, staurolite, kyanite, sillimanite, andalusite, cordierite, chlorite, plagioclase, alkali feldspar)Granulite facies: alkali feldspar plagioclase sillimanite quartz (biotite, garnet, kyanite, cordierite, orthopyroxene, spinel, corundum, sapphirine)Blueschist facies: phengite chlorite quartz (albite, jadeite, lawsonite, garnet, chloritoid, paragonite)Eclogite facies: phengite garnet quartz Mafic rocks (basalt, gabbro, diorite, tonalite etc.) yield a different set of minerals at the same P/T conditions, as follows: Zeolite facies: zeolite chlorite albite quartz (prehnite, analcime, pumpellyite)Prehnite-pumpellyite facies: prehnite pumpellyite chlorite albite quartz (actinolite, stilpnomelane, lawsonite)Greenschist facies: chlorite epidote albite (actinolite, biotite)Amphibolite facies: plagioclase hornblende (epidote, garnet, orthoamphibole, cummingtonite)Granulite facies: orthopyroxene plagioclase (clinopyroxene, hornblende, garnet)Blueschist facies: glaucophane/crossite lawsonite/epidote (pumpellyite, chlorite, garnet, albite, aragonite, phengite, chloritoid, paragonite)Eclogite facies: omphacite garnet rutile Ultramafic rocks (pyroxenite, peridotite etc.) have their own version of these facies: Zeolite facies: lizardite/chrysotile brucite magnetite (chlorite, carbonate)Prehnite-pumpellyite facies: lizardite/chrysotile brucite magnetite (antigorite, chlorite, carbonate, talc, diopside)Greenschist facies: antigorite diopside magnetite (chlorite, brucite, olivine, talc, carbonate)Amphibolite facies: olivine tremolite (antigorite, talc, anthopyllite, cummingtonite, enstatite)Granulite facies: olivine diopside enstatite (spinel, plagioclase)Blueschist facies: antigorite olivine magnetite (chlorite, brucite, talc, diopside)Eclogite facies: olivine Pronunciation: metamorphic FAY-sees or FAY-shees Also Known As: metamorphic grade (partial synonym)

Basswood Tree Description and Pruning Info

Basswood Tree Description and Pruning Info Introduction to the Basswood Tree Basswood, also known as American Linden is a large native North American tree that can grow more than 80 feet tall. In addition to being a majestic tree in the landscape, basswood is a soft, light wood and prized for hand carvings and making baskets. Native American basswood is found on rich, wet soils of the central and eastern United States. In the landscape, is a very beautiful and large tree with a majestic oval canopy mounted on a tall, straight trunk. Mid-summer brings abundant clusters of aromatic, yellow blooms which attract bees who make a prized honey - the tree is often fondly called the honey or bee tree. Taxonomy and Species Range The scientific name of basswood is Tilia americana and is pronounced TILL-ee-uh uh-mair-ih-KAY-nuh. Common names include American basswood, American linden and bee-tree and the tree is a member of the plant family Tiliaceae. Basswood grows in USDA hardiness zones 3 through 8 and is native to North America. The tree is often used as a hedge but only in large tree lawns. It grows rapidly, is very large and needs plenty of space. The tree makes an excellent landscape planting with limited tolerance to urban conditions depending on the cultivar. It is a perfect shade tree and can be used as a residential street tree. American Linden Cultivars There are several great cultivars of American linden including ‘Redmond’, ‘Fastigiata’ and ‘Legend’. The cultivar Tilia americana ‘Redmond’ grows 75 feet tall, has a beautiful pyramidal shape and is drought-tolerant. Tilia americana ‘Fastigiata’ is more narrow in shape with fragrant yellow flowers. Tilia americana ‘Legend’ is a hearty tree with resistant to leaf rust. The tree shape is pyramidal, grows with a single, straight trunk, and with upright, well-spaced branches. All of these cultivars are great as specimens for large lawns and along private drives and public streets. Pests of Basswood Insects: aphids are notorious pests on basswood but will not kill a healthy tree. Aphids produce a sticky substance called honeydew which then introduces a dark sooty mold that will cover objects under the tree including parked vehicles and lawn furniture. Other attacking insects include bark borers, walnut lace bug, Basswood leaf miner, scales and Linden mite can all be troublesome problems. Disease: Leaf rust is a major defoliator of basswood but some cultivars are resistant. Other diseases that infect basswood are Anthracnose, canker, leaf spots, powdery mildew, and verticillium wilt. Basswood Description: Basswood in the landscape grows to a height of 50 to 80 feet, depending on tree variety and site conditions. The trees crown spread is 35 to 50 feet and the canopy is typically symmetrical with a regular, smooth outline. Individual crown forms are consistent with an oval to pyramidal canopy shape. Crown density is tight and the trees growth rate is medium to rapid, depending on the site condition. Basswood Trunk and Branches Basswood branches droop as the tree grows and do require some pruning. If you have regular walking and vehicular traffic, a pruning may need to be done for clearance beneath the canopy. The tree form is not particularly showy but maintains a pleasing symmetry and should be grown with one single trunk to maturity. Basswood Leaf Botanics Leaf arrangement: alternateLeaf type: simpleLeaf margin: serrateLeaf shape: cordate; ovateLeaf venation: pinnateLeaf type and persistence: deciduousLeaf blade length: 4 to 8 inchesLeaf color: greenFall color: yellowFall characteristic: not showy I explain some of these terms in my Botanical Glossary... Necessary Site Conditions The native American basswood grows best on moist, fertile soils where those soils are acid or slightly alkaline. The tree likes to grow in full sun or partial shade and is more shade-tolerant than oaks and hickories. The leaves will show some wilting and scorching after a long dry season, but the tree appears fine the following year. The tree is often found growing along creeks and streams but will take short periods of drought. The trees favorite habitat is on moist sites. Pruning Basswood American linden grows into a very large tree and demands space to develop properly. Naturally occurring trees need no pruning but branches on landscape specimens should be spaced by pruning along the trunk to allow for development to maturity. Removing branches with weak crotches and embedded bark is advised even though the wood is flexible and will not often break from the trunk. Plant basswood as a specimen or shade tree only on property where there is plenty of area available for root expansion. Remember to remove basal sprouts that are prone to grow off the base of the trunk.