pleochroic halo

pleochroic halo
a dark-colored, microscopic ring around a minute radioactive particle in certain mineral crystals, used in estimating the age of the rocks containing these crystals

* * *

      ring of colour produced around a radioactive impurity included in a mineral by alpha particles (alpha particle) emitted from the radioactive elements in the inclusion. Because most of the energy of an alpha particle is absorbed at the end of its path length in a mineral, these colour centres are produced most intensely around the inclusion. The halos exhibit different colours when viewed in different directions because they differentially absorb light that vibrates in different directions. Pleochroic halos are commonly found in the minerals biotite, fluorite, and amphiboles (amphibole); the most common inclusions are the minerals zircon, xenotime, apatite, and monazite.

      The distance of the rings from the central radioactive inclusion depends upon the range of the alpha particles. Consequently, each ring may be identified with alpha emission by a specific element. Giant halos have been observed and cited as possible evidence for superheavy elements that emit very energetic alpha particles. It is generally believed that the giant halos result from some diffusion of the radioactivity and not from superheavy elements. The colour intensity of the ring diminishes with time and can be used to date the mineral in which the pleochroic halo appears.

* * *

Universalium. 2010.

Игры ⚽ Нужно решить контрольную?

Look at other dictionaries:

  • pleochroic halo — n. a dark colored, microscopic ring around a minute radioactive particle in certain mineral crystals, used in estimating the age of the rocks containing these crystals …   English World dictionary

  • pleochroic halo — noun a microscopic spherical region in which there is a change in colour from the surrounding mineral; due to radiation damage from alpha particles …   Wiktionary

  • pleochroism — /plee ok roh iz euhm/, n. the property of certain crystals of exhibiting different colors when viewed from different directions under transmitted light. Cf. dichroism (def. 1), trichroism. [1855 60; PLEOCHRO(IC) + ISM] * * * ▪ optics  (from Greek …   Universalium

  • John Joly — Infobox Scientist name = John Joly box width = image size =150px caption = John Joly birth date = November 1 1857 birth place = Bracknagh, County Offaly death date = December 8 1933 death place = Dublin, Ireland residence = citizenship =… …   Wikipedia

  • Allanite — from the Mt. Isa – Cloncurry area, Queensland, Australia (scale bar 1 inch) General …   Wikipedia

  • Radiohalo — Radiohalos are microscopic, spherical shells of discolouration in rocks, such as granite, or biotite caused by the inclusion of radioactive grains in the rock or by deposition of radioactive material in them. One widely accepted theory is that… …   Wikipedia

  • Радиоореол — Радиоореол[1] (англ. Radiohalo), плеохроический ореол[2][3] (англ. pleochroic halos)  микроскопическая шаровидная оболочка с изменённой окраской, встречающаяся внутри минералов, таких как биотит, содержащихся в гранитах и других… …   Википедия

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”