Taste can be used to distinguish halite (ordinary salt) from sylvite (which has some bitterness) and siltstone from mudstone (the latter has a creamy texture while the grains of the former can be felt). Are there other uses of taste for identification?
$\begingroup$ This question could use some tagging help. I was considering adding mineralogy, but was uncertain. There is no tag for methods (or field-methods), perhaps rightly so. $\endgroup$– Paul A. ClaytonJun 6, 2014 at 11:29
$\begingroup$ @plannapus I was thinking of asking a Meta question about whether something like field-methods (a.k.a., field-technique) would be a useful tag. petrology would be better than mineralogy. rock-identification would probably be a good tag for on-topic rock identification questions and techniques (though "identify this" is different from technique questions), but it does not yet exist. $\endgroup$– Paul A. ClaytonJun 6, 2014 at 12:31
$\begingroup$ Indeed you should maybe ask a meta question about the usefulness of field-method. In case you didn't know: you can create all the tags you want even if they don't exist just by adding them to a question. But it's nice indeed to ask for community input before flooding with tags :) $\endgroup$– plannapusJun 6, 2014 at 12:34
You are correct about halite and sylvite. I might add that carnallite also has an extremely bitter taste. These three minerals are chlorides and dissolve very easily, so that may be a part of the issue here. Differentiating mudstone (clay) from siltstone is actually not about taste, but rather about texture. Note that this can be misleading. If you have a rock with 70% clays and 30% sand (or silt), you are going to feel the silt, giving it a higher proportion in your estimate, unless you have enough experience to consider this bias.
I would also like to note the dangers in tasting rocks. Although not common, some minerals are radioactive. Also some minerals contain lead, mercury and other hazardous elements. Some minerals may also be contaminated by anthropogenic pollution. So be careful with tasting rocks.
I am frequently identifying as an engineering geologist grain size distribution of fine-grained cohesive soil by biting it (for almost 3 decades by now). With some experience one comes close to the actual grain size distribution determined in the lab. This is very useful when immediate decision is neccessary at a construction site.
Tasting rocks is done only if we already known that tasting would give us an answer about the rock type. We do not taste siltstones or sandstones because siltstone (and mudstone too) have no visible grains. On the contrary, sandstone has visible grains of sand. In most cases, when we try to identify a rock specimen in the field the tasting part is used very little.
The most common procedure is to lick or spit the specimen (I know is sounds a little weird), in order to see better the texture and probably to identify the minerals under sunlight. This is done only in fresh cuts, made by geological hammer. Some times, especially in carbonate rocks (limestones), we smell the sample right after cutting them, in order to detect bitumen.
Τhe dangers in tasting rocks is not coming by the rock itself, but by possible bacteria, fungi, Echinococcus, etc, from dirt, soil around it. Avoid testing any rock you collect, because it will not add anything to identification, but if like to do it anyway, do it ONLY in fresh cuts.