A sedimentary rock with only minerals?

Question

In my text book I came across this multiple-choice question>A sedimentary rock consists of only minerals and lacks fossils, it could be classified as:>i) a clastic sedimentary rock>ii) a chemical sedimentary rock>iii) a biochemical sedimentary rockOf course I would exclude "a biochemical", but I am confused between *clastic* and *chemical*. I did some research on google but didn't find a precise answer. However, I found that both of them could contain only minerals.So, I hope someone could help me here!

Answer 1

I find that question ambiguous and distasteful in the sense of being overly simplistic without being specific enough to answer properly. Either of the first two answers may be argued to be correct, and the third one can also be argued, with difficulty, to be correct. This said, I suspect the author of this question was expecting "chemical" to be the chosen one.

1. A sedimentary rock consisting only of the mineral quartz in sand-sized particles fits this description, and is a clastic sedimentary rock (it is also a detrital sedimentary rock).
2. A sedimentary rock consisting only of the mineral halite that formed as an evaporite deposit fits the bill, and is typically termed a chemical sedimentary rock.
3. A sedimentary rock consisting only of the mineral calcite in microscopic crystal form could fit the bill, depending on whether the microscopic calcite crystals can be called "fossils" or not. But it's not a very good answer for this particular, since if it is clearly a "biochemical" deposit, then it's almost fossiliferous by definition.