North American Auction Company
Timed Auction

Last Chance June 2023 Passed Lots Offering

Mon, Jun 5, 2023 02:00AM EDT - Fri, Jun 9, 2023 03:00PM EDT
Lot 724

Montana Agate Slabs & Texas Llanite Slab (4)

Estimate: $150 - $200

Bid Increments

Price Bid Increment
$25 $5
$50 $10
$100 $25
$500 $50
$1,000 $100
$2,000 $250
$5,000 $500
$10,000 $1,000
$25,000 $2,500
For your consideration is this lot of three agate slabs and one Llanite slab from Texas. Llanite is a porphyritic rhyolite with distinctive phenocrysts of blue quartz (a rare quartz color) and perthitic feldspar (light grayish-orangish). The brown, fine-grained groundmass consists of very small quartz, feldspar, and biotite mica crystals. The Llanite slab shows colors of brown, brown/red, orange, blue and purple throughout the slab. The first agate slab shows a highly polished and smoothed look with colors of brown, grey, light blue and white. The second agate slab has smoothed sides and one side being highly polished. It shows a more rocky outer layer than the first one, with the agate in the center showing colors of cloudy light blue, grey and white. The third and largest agate slab in this lot shows smoothed sides with one side being highly polished. On the unpolished side it reads, "Limb Cast Montana" showing that the agate was found in Montana and the agate was formed in a tree limb. Limb Casts are created when agate is deposited in cavities formed by tree branches covered by volcanic ash. The wood burns away after being covered by the hot ash. Under the right conditions agate fills the empty space. The result is a piece of agate that has the form of a tree limb, hence the name limb Cast. This piece of agate shows stripped colors of white, grey, beige, light blue and tan. All the pieces in this lot show good condition with no signs of obvious damage. The Llanite slab measures 4 3/4" L x 6 1/2" W, The smallest agate slab measures 3 13/16" L x 3 1/2" W, while the largest agate slab measures 4 1/2" L x 5 1/4" W.