New Mexico Mineral Symposium — Abstracts

The Big Lue Mountains of eastern Arizona and western New Mexico offer several good collecting opportunities for the micromounter. Good micromount specimens have been found in several localities near the state line along New Mexico and Arizona State Highway 78 west of Mule Creek, New Mexico.

The Big Lue Mountains are composed of Tertiary rhyolitic volcanics and younger Tertiary basaltic volcanics as flows and tuffs. The volcanics are often vesicular and host two distinct suites of minerals of interest to collectors. Minerals found in the older volcanics are similar to the Black Range topaz-bearing rhyolites and include:
pseudobrookite

• titanite
• hematite
• tridymite
• phlogopite
• hollandite

Several unidentified minerals are present but they appear to be pseudomorphs after an undetermined mineral. Pseudobrookite is fairly common, occurring as slender elongated euhedral blades that are rarely over two mm long. Titanite is also common, occurring as very small, equant, transparent, reddish-orange crystals. Hematite is common as small blocky to thin lustrous black crystals rarely over two mm in size. Tridymite is found in nearly every vesicle in some places and occurs as multiply twinned crystals up to one cm across. Phlogopite occurs as thin, transparent, light-brown crystals up to 4 mm across. Hollandite is locally abundant as black dendritic growths and coatings in vesicles and overgrowths on some of the other minerals.
The younger volcanics host a suite of zeolites and associated minerals that include:

• erionite-offretite
• heulandite
• mesolite(?)
• quartz
• calcite

These minerals are more sparsely distributed but locally abundant. Heulandite and erionite-offretite occur as small euhedral crystals in vesicles. A mineral that resembles mesolite is sometimes found with calcite and quartz.

The localities examined so far have been in roadcuts or along stream banks. There are many unexplored hills, cliffs, and streams that may yield additional species.