PALS - Rubric

Minerals

Rubric

Contributed by: Council of Chief State School Officers (CCSSO/SCASS)

The important thing about the mineral identification is that whichever mineral is scratched by the softest thing should be ãtalcä (pyrite). The hardest mineral shouldnât be scratched by anything, therefore it is quartz, and the other two should be ranked softer (calcite) and harder (hornblende).

There are no instructions about wiping the area that was just scratched so that you can tell whether the marks or flakes are from the mineral or the scratching tool, so many students will report unexpected results in Table A. This will lead to a variety of responses in Table B. For example, students may report that the nail scratched the quartz (mineral B) when what they really saw was the streak of steel left on the quartz by the nail. Mineral A (calcite) may appear to be scratched by the fingernail if nail scrapings adhere to it. Mineral D (pyrite) may be in a very crumbly matrix and therefore appear to be scratched by a fingernail because some of the sandy grains come loose.

For scoring purposes, the important points are that the studentsâ identifications of the samples follow from their own scratch test results and the bar graph information.

Rubric

1. In table B, the student identifies as talc whichever mineral appeared to be softest based on the results of the student's scratch test. If two minerals appear identically softest from the scratch test, either may be called talc in table B, but to meet this criterion the other must be identified as calcite, since it is the nearest in softness to talc. If three or more minerals appear identically soft from the scratch test, do not examine table B.

2. In table B, the student identifies as quartz whichever mineral appeared to be hardest based on the results of the scratch test. If two minerals appear identically hardest based on the results of the student's scratch test, either may be called quartz in table B, but to meet this criterion the other must be identified as hornblende, since it is the nearest in hardness to quartz. If three or more minerals appear to be identically hardest from the scratch test results, do not examine table B.

3. In response to question 2, the student chooses a mineral based on its hardness. Texture is not an acceptable basis for "best mineral" selection.

4. The student selects quartz as the best mineral for sandpaper, because it is hardest.

Note: If the student chooses a mineral by its letter, and identified it as quartz in table B, but that identification did not follow from the scratch test results, do not give credit for this criterion.
OR
If the student chooses a mineral other than quartz, the student clearly knows the chosen mineral is not the hardest but has a well-reasoned defense.