Thursday, June 12, 2008

"Because You Asked"

June's mineral of the month, Calcite, elicited a fair amount of oohs and aahs, as members and guests had an opportunity to examine the several beautiful and extremely different examples of this relatively common mineral. Hopefully this new feature of the Del-Air Rockhounds Club is being enjoyed and we are all learning something new.

This brings us to yet another new feature of the club, "Because You Asked". If anyone ever has a question regarding rocks, minerals or other rock hounding subjects that can not be answered while at our monthly meetings, simply e-mail your question to Bob Knox at: or Chris Ward at: and your query will be researched and answered right here in your blog. Questions may be submitted at any time and members and interested guests will receive an e-mail notification stating the answers have been posted to the blog.

And now....for our first question....

Mrs. Paul O'Connor asks...."In the information handout for the June 2008 Mineral of the Month, Calcite, the word 'gangue' appeared in the mineral's description. What does this word mean?

"Because You Asked" answers:

Ore and Gangue: The general definition of “ore” is a naturally occurring material from which minerals of economic value can be extracted at a profit. For example “gold ore” or “iron ore”. Ore minerals are the specific minerals containing the commodity of interest. Many minerals contain elements of commercial interest, but are not ore minerals because the mineral is “refractory”, meaning it is difficult or impossible to extract the commodity from the mineral. Gangue (pronounced like 'gang') minerals refer to the material so intimately associated with the ore that it has to be mined along with the ore and is later removed by various crushing, grinding and separation processes. The “host rock” is the rock surrounding the ore and gangue, which has no value. To illustrate these relationships, consider the following example for a gold ore:

A gold-bearing quartz vein 1 foot thick occurs in a granite intrusion. The quartz vein contains arsenopyrite and pyrite in addition to native gold. The “ore” in this example is the quartz vein that contains concentrations of gold. The ore mineral is the native gold. The gangue minerals are quartz, arsenopyrite and pyrite. The granite is the host rock.

Thanks for the questions and keep them coming!!