Hi Cecile,

That is a excellent direct question...Thank you.

I'm not near all my books at the moment...but I think Hoadley's "Understanding Wood" may mention it or the Genus having such a characteristic...???...but can state for sure.

I think most of my assertions of this is from personal direct experience and speaking with others like yourself, who actually take the time understand the species more empirically themselves.

Since you asked (and I haven't look at this topic in a while...LOL) some quick searches refreshed my understanding:

Silica (SiO2) content in wood species is determined by incineration of a wood sample and weighing ash for the differential between the volatile compound silicon tetrafluoride (SiF4) following the Tappi Standard T-15 and ASTM Standard D 1102...as I understand it...???...but there could be others modalities of testing outside my scope of understanding? I will share that these in depth laboratory analyses are way outside my world of expertise or ability to do myself and I leave it to others to do such testing.

I understand that temperate forest species are less prone to higher silica content than tropical and that equal to or greater than 0.5% silica in wood is the harmful range to most edged tools (...it would seem??)...If Robinie has this range in some population samples is not confirmed scientifically from what I just found with a quick search.

It has been compared to Angelique (Dicorynia guianensis) which does have high silica content as a tropical species ( U.S. FOREST SERVICE RESEARCH NOTE FPL-07...ts Technologist ), yet mineral inclusion of silica where not observed by H.G. Richter and M.J. Dallwitz ( Commercial timbers H.G. Richter and M.J. Dallwitz Robinia pseudoacacia L. (Robinie, black locust) .)

Thus far, with this current quick search, I haven't found specific testing or papers related to silica content as would be measured (scientifically) by any of the recognised testing modalities or standards as thus described.

The folks at Rockbridge Trees state: " For woodworkers, the rot resistance comes from the silica deposits in the wood..." yet they provide no resource reference to this determination and could just be repeating information from other unconfirmed sources?

Because the Robinia ssp can and often does grow under adverse edaphic conditions, which many rot resistant tree species often due...silica content being higher could be a result of this or just a presumption? I question my own full understanding of this now myself...other than my empirical determination that know tropical species with high silica content "feel and act" much like Locust...at least to me it does?

I did further learn on this search that older trees do indeed have better durability than juvenile (under ten years) like many other rot resistant species of tree. So felling cycles are well advised to exceed this in good forestry management plans. Locust Borer (Megacyllene robiniae), susceptibility to "witches broom" (virus Cholorogenus robinia) as well as heartwood/canker diseases from fungal infection could also effect the silica and/or rot resistant characteristics of a given population within a forest? Yet this seems to be more about lumber yield issues rather than affecting decay resistance. I have experienced, read (and heard) that stresses like this can enhance such decay resistance in many species, but no scientific papers at this time to support that supposition...just my own experiences with wood.

Thanks for asking the question...

j