The common causes are metal ions, intervalence charge transfer, ionizing radiation, physical effects, and band gaps.

1) Metal ions cause the color of many common and uncommon minerals.

2) Intervalence Charge Transfer, involving metal ions in mixed oxidation states is another important factor in the coloration of minerals. Most commonly, we encounter minerals with the Fe2+ - Fe3+ interaction and with the Fe2+ - Ti4+ interaction.

3) Colors from natural ionizing radiation are frequently encountered in nature. Most common minerals have had a long history of exposure to ionizing radiation from natural radiation sources in rocks. A variety of minerals can also be colored by artificial irradiation which enter the commercial market in the form of colored gemstones.

4) Physical effects such as diffraction also cause colors in minerals. The color of gem opal is the result of diffraction as is the color of certain crystals of labradorite feldspar.

5) Semiconducting minerals have band gaps which often result in intense colors. Numerous sulfides are examples of this.

To find information about the causes of color in minerals visit the web at: http://geology.about.com/cs/mineralogy/

Once at the web site, follow the link on the left for Mineralogy, which provides illustrations of many examples.

Final meeting for presenting the slide show on the revision process:

Androscoggin/Evans Notch District Area

Thursday, March 14, 7-9 PM

Androscoggin Ranger District Office

300 Glen Road off Rte 16, Gorham, NH

We want to thank you for the time spent attending LPG meetings. It’s been great to have your input on the revision topics.

We will continue working to finalize the analysis of the management situation and develop programmatic issues for our next round of meetings. You will receive updates in future flyers about new information that is available and the next round of meetings.

Thanks from the planning team