Tuesday, February 27, 2007

Minerals and rocks

A mineral is a obviously occurring, inorganic solid with a definite chemical composition and a crystalline structure. A rock is an collective of one or more minerals. (A rock may also include organic remains and mineraloids.) Some rocks are mostly composed of just one mineral. For example, limestone is a sedimentary rock composed almost wholly of the mineral calcite. Other rocks have many minerals, and the specific minerals in a rock can vary widely. Some minerals, like quartz, mica or feldspar are general, while others have been found in only one or two locations worldwide. The vast majority of the rocks of the Earth's crust consist of quartz, feldspar, mica, chlorite, kaolin, calcite, epidote, olivine, augite, hornblende, magnetite, hematite, limonite and a few other minerals.Over half of the mineral species identified are so rare that they have only been found in a handful of samples, and many are known from only one or two small grains.
Commercially costly minerals and rocks are referred to as industrial minerals. Rocks from which minerals are mined for economic purposes are referred to as ores (the rocks and minerals that remain, after the desired mineral has been separated from the ore, are referred to as tailings).

Thursday, February 22, 2007

Acid rain

Acid rain occurs when sulphur dioxide and nitrogen oxides are emitted into the atmosphere, undergo chemical transformations and are absorbed by water droplets in clouds. The droplets then fall to earth as rain, snow, mist, dry dust, hail, or sleet. This can add to the acidity of the soil, and affect the element balance of lakes and streams.The term "acid rain" is sometimes used more usually to include all forms of acid deposition - both wet deposition, where acidic gases and particles are removed by rain or other precipitation, and dry deposition removal of gases and particles to the Earth's surface in the absence of precipitation. Acid rain is defined as any type of precipitation with a pH that is abnormally low. Dissolved carbon dioxide dissociates to form weak carbonic acid giving a pH of approximately 5.6 at typical atmospheric concentrations of CO2. Therefore a pH of less than 5.6 has every so often been used as a definition of acid rain. However, natural sources of acidity mean that in remote areas, rain has a pH which is between 4.5 and 5.6 with an average value of 5.0 and so rain with a pH of less than 5 is a more appropriate definition. The US EPA says, "Acid rain is a serious environmental problem that affects large parts of the US and Canada" Acid rain accelerates weathering in carbonate rocks and accelerates building weathering. It also contributes to acidification of rivers, streams, and forest damage at high elevations. When the acid builds up in rivers and streams it can kill fish.

Sunday, February 18, 2007


Historiography has a number of associated meanings. It can refer to the history of historical learning, its methodology and practices (the history of history). It can also refer to a particular body of historical writing (for example, "medieval historiography during the 1960s" means "medieval history written during the 1960s"). Historiography can also be in use to mean historical theory or the study of past writing and memory. As a meta-level analysis of descriptions of the past, this third conception can relate to the first two in that the analysis usually focuses on the narratives, interpretations, worldview, use of evidence, or method of presentation of other historians.

Sunday, February 11, 2007


Gardening is the art of growing plants with the aim of crafting a purposeful landscape. Residential gardening most often takes place in or about a residence, in a space referred to as the garden. Although a garden naturally is located on the land near a residence, it may also be located in a roof, in an entrance, on a balcony, in a windowbox, or on a yard.
Gardening also takes place in non-residential green areas, such as parks, public or semi-public gardens (botanical gardens or zoological gardens), pleasure and theme parks, along transportation corridors, and around tourist attractions and hotels. In these situations, a staff of gardeners or groundskeepers maintains the gardens.
Indoor gardening is concerned with the increasing of houseplants within a residence or building, in a conservatory, or in a greenhouse. Indoor gardens are sometimes included as part of air conditioning or heating systems.
Water gardening is concerned with growing plants adapted to pools and ponds. Bog gardens are also considered a type of water garden. These all require extraordinary conditions and considerations. A simple water garden may consist simply of a tub containing the water and plant(s).
Container gardening is concerned with growing plants in any type of container either indoors or outdoors. Common containers are pots, hanging baskets, and planters. Container gardening is usually used in atriums and on balconies, patios, and roof tops.

Monday, February 05, 2007

Public transport

Public transport, public transportation, public travel or mass transit comprises all transport systems in which the passengers do not tour in their own vehicles. While it is generally taken to include rail and bus services, wider definitions would comprise scheduled airline services, ship, taxicab services etc. – any system that transports members of the universal public. A further restriction that is sometimes practical is that it must take place in shared vehicles that would bar taxis that are not shared-ride taxis.