The chemical inertness of a geologic material depends upon the inertness of the minerals of which it is composed. If the inertness of the individual minerals and the percentages of those minerals are known, an "inertness value" (IV) for the material as a whole may be calculated.

If you wish to review the Mineral Inertness 'rollover', click on the blue button.
It is apparent that with the exception of calcite, which has an intermediate inertness, all the minerals found in the NYC area (listed on the right next, to the brown column) are highly inert. Numerical equivalents may be assigned to inertness:

  • highly inert
    (H) = 7;
  • intermediate inertness
    (I) = 3;
  • low inertness
    (L) = 1.

To determine Inertness Values for the NYC rocks and sediments, follow these steps (see example):

  1. Print out a copy of the 'Inertness Value Calculation Table' (printout # Q-4).
  2. For each rock or sediment, enter its percentage of calcite and its total percentage of minerals other than calcite in rows (a) and (b). (Obtain these percentages from printout #Q-1A, the Mineral Composition Tabulation Sheet.)
  3. Enter the total of the percentages of calcite and other minerals in row (c). It should equal 100.
  4. Multiply the % calcite times 3 (the numerical equivalent of its inertness) and enter the result in row (d).
  5. Multiply the % other minerals times 7 (the numerical equivalent of their inertness) and enter the result in row (e).
  6. Add together the values in rows (d) and (e) and enter the sum in row (f).
  7. Divide the value in row (f) by 100. Round off the result to two decimal places. Enter this number in row (g). This number is the Inertness Value for the material.
# Q-4


1. Click on the pink button and print out one copy of the 'Inertness Value Calculation Table', (printout # Q-4).
2. Determine the Inertness Value of each of the eight NYC geologic materials: diabase, gneiss, marble, sandstone, shale, schist, Long Island Hill Sediment, Long Island Plain Sediment.
3. Click on the 'Inertness Value Checking Table' button to see if your Inertness Values are correct.
4. Record all eight Inertness Values in column (b) of the Erosion-Resistance Index Calculation Table (printout #Q-6).

David J. Leveson