Quartz dissolution associated with magnesium silicate hydrate cement precipitation
<p>Quartz has been replaced by magnesium silicate hydrate cement at the Feragen ultramafic body in south-east Norway. This occurs in deformed and recrystallized quartz grains deposited as glacial till covering part of the ultramafic body. Where the ultramafic body is exposed, weathering leads...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-02-01
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| Series: | Solid Earth |
| Online Access: | https://se.copernicus.org/articles/12/389/2021/se-12-389-2021.pdf |
| Summary: | <p>Quartz has been replaced by magnesium silicate hydrate cement at
the Feragen ultramafic body in south-east Norway. This occurs in deformed
and recrystallized quartz grains deposited as glacial till covering part of
the ultramafic body. Where the ultramafic body is exposed, weathering leads
to high-pH (<span class="inline-formula">∼</span> 10), Mg-rich fluids. The dissolution rate of the
quartz is about 3 orders of magnitude higher than experimentally derived
rate equations suggest under the prevailing conditions. Quartz dissolution
and cement precipitation start at intergranular grain boundaries that act
as fluid pathways through the recrystallized quartz. Etch pits are also
extensively present at the quartz surfaces as a result of preferential
dissolution at dislocation sites. Transmission electron microscopy revealed
an amorphous silica layer with a thickness of 100–200 nm around weathered
quartz grains. We suggest that the amorphous silica is a product of
interface-coupled dissolution–precipitation and that the amorphous silica
subsequently reacts with the Mg-rich, high-pH bulk fluid to precipitate
magnesium silicate hydrate cement, allowing for further quartz dissolution
and locally a complete replacement of quartz by cement. The cement is the
natural equivalent of magnesium silicate hydrate cement (M-S-H), which is
currently of interest for nuclear waste encapsulation and for environmentally
friendly building cement, but it has not yet been developed for commercial use. This
study provides new insights that could potentially contribute to the further
development of M-S-H cement.</p> |
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| ISSN: | 1869-9510 1869-9529 |