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Rocks are the primary source of all plant nutrients, except nitrogen. These nutrients are bound into a variety of crystalline structures (minerals). Minerals are either formed during rock formation from magma (primary mineral) or formed during soil formation (secondary minerals). Secondary minerals are formed when the local soil solution is saturated in respect to that mineral. In contrast to secondary minerals, for primary minerals the soil solution is generally undersaturated, causing these minerals to dissolve. But this dissolution process is extremely slow for most minerals. It has been estimated that it takes more than 30 million years to dissolve a 1 mm diameter quartz grain under natural soil conditions conditions  data-bib-text="@article{Lasaga_1984, doi = {10.1029/jb089ib06p04009},  url = {http://dx.doi.org/10.1029/jb089ib06p04009},  year = 1984, 

author = {Antonio C. Lasaga},  title = {Chemical kinetics of water-rock interactions},  journal = {J. Geophys. Res.}  }" data-bib-key="Lasaga_1984"style="cursor: pointer"  contenteditable="false">class="au-cite-link"  href="#Lasaga_1984">Lasaga 1984. Nonetheless, soil mineral weathering provides an essential input of plant nutrients into ecosystems, avoiding or delaying nutrient limitations limitations  data-bib-text="@article{Chadwick_1999, doi = {10.1038/17276},  url = {http://dx.doi.org/10.1038/17276},  year = 1999, 

pages = {491--497},  author = {O. A. Chadwick and L. A. Derry and P. M. Vitousek and B. J. Huebert and L. O. Hedin},  journal = {Nature}  }" data-bib-key="Chadwick_1999"style="cursor: pointer"  contenteditable="false">class="au-cite-link"  href="#Chadwick_1999">Chadwick 1999.

In addition, mineral weathering produces cations that counteract soil acidification, thereby improving the availability of most plant nutrients nutrients  data-bib-text="@article{van_Breemen_1983, doi = {10.1007/bf02369968},  url = {http://dx.doi.org/10.1007/bf02369968},  year = 1983, 

author = {N. van Breemen and J. Mulder and C. T. Driscoll},  title = {Acidification and alkalinization of soils},  journal = {Plant Soil}  }" data-bib-key="van_Breemen_1983"style="cursor: pointer"  contenteditable="false">class="au-cite-link"  href="#van_Breemen_1983">Breemen 1983. Also clays are formed as a weathering product of feldspars and micas micas  data-bib-text="@article{Oades_1988, doi = {10.1007/bf02180317},  url = {http://dx.doi.org/10.1007/bf02180317},  year = 1988, 

author = {J. M. Oades},  title = {The retention of organic matter in soils},  journal = {Biogeochemistry}  }" data-bib-key="Oades_1988"style="cursor: pointer"  contenteditable="false">class="au-cite-link"  href="#Oades_1988">Oades 1988. Clay particles contribute, with their negative charged surfaces, to the cation exchange capacity (CEC) of the soil, reducing the leaching of positively charged nutrients like K+
 K+ and NH4+. Clay content correlates positively with water holding capacity and soil organic matter (SOM) contentSollins 1996.

Moreover, the weathering of Ca- and Mag-silicate minerals play a central role in the global carbon cycle. The Ca and Mg, released by the weathering process, will be locked up as carbonates in marine sedimentsSundquist 1985. On the long-term, atmospheric CO2 is regulated by the weathering rates of these minerals, which is influenced by climate and mountain upliftBerner 2003Raymo 1992.

The vast amounts of nutrients locked in soil minerals has triggered, nearly 100 years ago, the question if plants actively enter this potential nutrient sourceHALEY 1923TURK 1919. Five decennia later, studies appear on the role of microorganisms, including mycorrhizal fungi, in mineral weatheringWEBLEY 1963DUFF 1963Sperber 1958Boyle 1967Boyle 1973. More recently, a publication with the provocative title Rock eating fungi appeared in NatureJongmans 1997. This publication presented evidence of, presumably mycorrhizal, fungal hyphae drilling their way (chemically and/or physically) into feldspar grains. This paper initiated renewed interest into the topic. A series of reviews has been published since then, covering the research up to 2009Finlay 2009Hoffland 2004Landeweert 2001.