Friday, April 29, 2011

Dunite - Decorative, Heat Resistant and CO2 Sequestration

Visiting a local office in Bellingham today I noted the counter of the reception area was made from slabs of dunite.
Dunite counter top.

Later walking to the post office and courthouse for mail and research I saw a dunite bench along the Whatcom Creek trail.

Dunite bench along Whatcom Creek trail

Dunite is the from the earth's mantle and consists primarily of olivine. Dunite and other rocks with high iron and magnesium content are called ultramafite. The Twin Sisiters range in the Northwest Cascades consists almost entirely of dunite. The range is essentially a huge block of the earth's mantle somehow exhumed and thrust up into the Northwest Cascade Range (twin-sisters-range-and-dunite). A quarry on the lower slopes of the range extracts dunite as a liner for high temperature incinerators as olivine has a high melting temperature (its from the mantle of the earth). The rock is attractive so is also commonly used as a decorative stone. The downside of its use as decorative rock is that it is very hard and very massive with a specific gravity approximately twice that of average rocks. 

Ultramafic rocks such as dunite have gained interest as a means of sequestration of CO2 by the reaction Mg2SiO4 (Mg Olivine) + 2CO2 ---> 2MgCO3 (magnesite) + SiO2.  See Danae and others (2009) for an over view of site selection and Koukouzas and others (2009) for a bench study.  

In both examples above I like the orange weathering rind left on the edge of the counter and bench. This is the same color as the Twin Sisters range when the range is not mantled in snow as it was last week when I saw the range from near the South Fork Nooksack Valley. 

Twin Sisters viewed from Saxon


Sam Crawford said...

Dan, a long time ago someone from Woodstone (who started out in Sumas using this material for their pizza ovens, although I believe for a long time now they've been using a different manufactured composite material) told me that this source of olivine was unique and comparable in quality and quantity to only one other place in the world, I think it was a mountain range in Turkey. Do you know if I've got that straight, or is my memory jumbled here?

Dan McShane said...

I would not be surprised if there is a dunite block in Turkey. The Twin Sisters is a remarkable uniform block. I do know that there is a larger dunite area in Russia. As to quality or uniformity I am not well versed.

Dave Wenning said...

Is dunite the stone seen all over Fidalgo Island, especially in Deception Pass State Park?

Dan McShane said...


No, but there are mafic to ultramafic rocks on Fidalgo that are a likely ophiolite complex - that is a slab of ocen floor crust including some deep crustal layers. These rocks are very Magnesium enriched. But no dunite which is even deeper being mantle rock. It is dificult to get a chunk of mantle wedged up to the surface, but dunite association with ophiolite would not be unreasonable.

Anonymous said...


I was wondering if it allowed to mine for Dunite at Twin Sisters? Thanks

Dai said...

Theres dunnite in Nelson New Zealand also, on a local mineral belt. 80tons was mined last century and confirmed as an excellent heat resistant material, and subsequently sent onto Detroit to use in steel furnaces prior to WW2.