Vein (geology)

In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved is usually due to hydrothermal circulation.

Veins are classically thought of as being the result of growth of crystals on the walls of planar fractures in rocks, with the crystal growth occurring normal to the walls of the cavity, and the crystal protruding into open space. This certainly is the method for the formation of some veins. However, it is rare in geology for significant open space to remain open in large volumes of rock, especially several kilometers below the surface. Thus, there are two main mechanisms considered likely for the formation of veins: open-space filling and crack-seal growth.

Open space filling

Open space filling is the hallmark of epithermal vein systems, such as a stockwork, in greisens or in certain skarn environments. For open space filling to take effect, the confining pressure is generally considered to be below 0.5 GPa, or less than 3-5 kilometers. Veins formed in this way may exhibit a colloform, agate-like habit, of sequential selvages of minerals which radiate out from nucleation points on the vein walls and appear to fill up the available open space. Often evidence of fluid boiling is present. Vugs, cavities and geodes are all examples of open-space filling phenomena in hydrothermal systems.

Reef knot

The reef knot, or square knot, is an ancient and simple binding knot used to secure a rope or line around an object. It is sometimes also referred to as a Hercules knot. The knot is formed by tying a left-handed overhand knot and then a right-handed overhand knot, or vice versa. A common mnemonic for this procedure is "right over left; left over right", which is often appended with the rhyming suffix "... makes a knot both tidy and tight". Two consecutive overhands of the same handedness will make a granny knot. The working ends of the reef knot must emerge both at the top or both at the bottom, otherwise a thief knot results.

Although the reef knot is often seen used for tying two ropes together, it is not recommended for this purpose because of the potential instability of the knot, and over-use has resulted in many deaths (see #Misuse as a bend).

Naming

The reef knot is at least between 4,000 and 9,000 years old. The name "reef knot" dates from at least 1794 and originates from its common use to reef sails, that is to tie part of the sail down to decrease its effective surface area in strong winds. To release the knot a sailor could collapse it with a pull of one hand; the sail's weight would make the collapsed knot come apart. It is specifically this behavior which makes the knot unsafe for connecting two ropes together.

Reef (disambiguation)

Reef may refer to:

See also

Lately

"Lately" may refer to:

Lately (Skunk Anansie song)

"Lately" is a song by Skunk Anansie, released as the third single from their album Post Orgasmic Chill. It was released in August 1999. CD1 came with an interactive element featuring the video and CD2 featured three exclusive Polaroid pictures of the band. As of 2012, it is the band's last major hit, charting at #33 in their native United Kingdom.

Music video

The surreal music video was directed by Howard Greenhalgh, who directed the music video for "Goodbye" by Spice Girls, a year earlier. The music video shows the band performing in a small town where all its inhabitants are smiling while a comet (played by Skin) begins to have a collision course with Earth. The video for the single was a homage to Soundgarden's music video for "Black Hole Sun", which was also directed by Greenhalgh in 1994.

Track listing

CD single - CD1

CD single - CD2

Notes

External links

Lately (album)

Lately is the studio album by the Contemporary Christian and gospel singer Raymond Cilliers.It was released on the label Brettian Productions in 2005.

Track listing

Single

References