Typical porosities of geologic materials Which of the following statements about porosity values is incorrect?

Introduction / Context:Porosity is the ratio of void volume to total volume and governs storage of groundwater and the compressibility of soils/rocks. Typical ranges vary by material and compaction state.

Given Data / Assumptions:

• Values quoted are indicative typicals, not absolutes.
• Materials considered: clayey sand, clean sand, sandstone, and crystalline rocks.

Concept / Approach:Clayey mixtures can exhibit relatively high porosity (often 40–50% or more). Clean sands commonly range 25–40% depending on gradation/packing. Sandstones may exhibit porosity from very low to over 20%, but “up to about 15%” is a reasonable indicative figure for compact sandstone. Dense crystalline rocks like granite and quartz generally have very low primary porosity.

Step-by-Step Solution:

Verification / Alternative check:Hydrogeology references list similar ranges: sands 25–40%, sandstones often 5–20% (variable), and crystalline rocks near-zero primary porosity.

Why Other Options Are Wrong:Each individual statement reflects plausible typical values; therefore singling any one as incorrect would be unjustified.

Common Pitfalls:Confusing porosity with permeability; high porosity (clays) may still have very low permeability.

Final Answer:None of these