Larimar tarnish, oxidation?

I have been working with larimar for the past 12 months or so and
have generally been happy with the results. I have mostly been
working with high quality rough (deep blues, few if any fractures,
very few patches of the dark gray matrix). However, some of my rough
appears to oxidize? once it is exposed to water ( I use a synthetic
oil/water lubricant [lube 4800] with the saw, straight water (soft)
for grinding, and diamond for polishing).

What I find is that brown/rust orange plumes begin to infuse the
surface and then the interior of the stone. It looks rather like the
plumes of a plume agate, however it is very undesirable to see a
beautiful piece of valuable deep blue solid larimar become ruined
with plumes of reddish/rust brown color. The process sometimes only
takes 15 or 20 minutes to become noticeable, and the plumes can
eventually cover the surface of a 2 inch square slab. These plumes
usually start from the outer edges of the stone, I believe they may
be some sort of tarnish or oxidation (iron oxide?) from impurities
in the stone that is reacting with the water. However there does not
appear to be any rhyme or reason to the appearance of the brown
plumes - I have tumbled a batch of end cuts and pieces and there was
not a sign of any discoloration (and these pieces were in water
polish slurry for a month!)

Has anyone had a similar experience with larimar? Any thoughts on
how to avoid the formation of this oxidation/tarnish (it would be
difficult for me to polish only with oil based lubricant - not sure
if that would work anyway)? Is there some way of “clearing up” or
treating the brown plumes perhaps with acid??? Any thoughts or help
would be greatly appreciated.


Hi John,

I’ve encountered something similar with other materials (ie;
amazonite) and have considered using oxalic acid to see if that might
"get the red out". It works on crystals so may be worth a try on a
scrap piece of your stone. If anyone else has experimented with this
I’m curious to know what the result was too.

Looking forward to seeing the other suggestions to your great question!

Hi John,

While I do very little larimar no pieces that I’ve done have ever
reacted in this way. If it were an oxidation process on something
inherent in the stone one would expect slabs also to eventually
degrade. They do not (at least mine don’t).

Therefore it seems logical suspect as culprit some foreign material
that has been introduced into the stone. The candidate that
immediately comes to mind is the oil part of the synthetic oil/water
sawing lubricant seeping into the bundles of pectolite fibres. It is
conceivable also that you may have a high iron mineralized water in
your area but that’s a distant second rank consideration. Oil is by
far likelier. I may be wrong but I have a very strong suspicion that
the problem would disappear if you used water and nothing but all the
way through.

Hans Durstling
Moncton, Canada

What I find is that brown/rust orange plumes begin to infuse the
surface and then the interior of the stone. 

I have been working with top grade Larimar for several years now and
I have never have that happen to me. I use only water,no oil, when I
saw it. Might that be the reason? Somehow I doubt it. Then I grind
down using diamond sintered laps, 220 and 1200 with water, and I
polish using olive oil mixed with diamond grit. 1200, then 14000,then
50,000 then, if it is a really good piece, 100,000 grit. ( for that
‘wet’ look) My gut feeling is that you picked up a bum parcel, maybe?
The atmosphere here in St Maarten is immensely corrosive, so much so
that 18ct tarnishes in weeks and tools rust with wild abandon. So far
all my larimar has behaved as is should. I would love to see a
picture of your discolored Larimar. Forewarned and all that stuff.
High season is coming up and then the Dominican sellers come round
I’ll ask about this, for sure. I’ll post what they say. Quite
worrying, I must say. Also another thing that I heard is that
Larimar is photosensitive, and that it fades in sunlight. I put a
piece in sunlight for a while now and there is no visible difference
with the control piece.Yet… I would be less than popular if some of
my carved stuff did a wobbly, I tell you.I only set my stuff in 18ct
and it’s not cheap. It would be quite difficult to sell a piece and
then tell the lady she can only wear it at midnight…

Cheers, Hans Meevis