Condensed-matter physics, discipline that treats the thermal, elastic, electrical, magnetic, and optical properties of solid and liquid substances.

Among solid materials, the greatest theoretical advances have been in the study of crystalline materials whose simple repetitive geometric arrays of atoms are multiple-particle systems that allow treatment by quantum mechanics. Because the atoms in a solid are coordinated with each other over large distances, the theory must go beyond that appropriate for atoms and molecules. Thus conductors, such as metals, contain some so-called free (or conduction) electrons, which are responsible for the electrical and most of the thermal conductivity of the material and which belong collectively to the whole solid rather than to individual atoms. Semiconductors and insulators, either crystalline or amorphous, are other materials studied in this field of physics.

Other aspects of condensed matter involve the properties of the ordinary liquid state, of liquid crystals, and, at temperatures near absolute zero (−273.15 °C, or −459.67 °F), of the so-called quantum liquids. The latter exhibit a property known as super fluidity (completely frictionless flow), which is an example of macroscopic quantum phenomena. Such phenomena are also exemplified by superconductivity (completely resistance-less flow of electricity), a low-temperature property of certain metallic and ceramic materials. Besides their significance to technology, macroscopic liquid and solid quantum states are important in astrophysical theories of stellar structure in, for example, neutron stars.

Cited from https://www.britannica.com/science/condensed-matter-physics

A phase diagram links any two state variables, e.g. pressure and temperature, and shows regions in which a substance in equilibrium is in a uniform state, i.e. the local structure of all its atoms or molecules is identical. An amount of material in a uniform state is referred to as a phase: a glass of water with ice cubes in it contains water in its liquid and solid states, and the liquid and the ice cubes are one phase each. The single-phase regions are separated by phase transition lines. At each point along such a line, the two phases are in equilibrium with each other - atoms/molecules can cross from one phase to the other, but it is a two-way process. Changing one state variable externally will force the other one to respond if equilibrium is maintained. At the triple point, solid, liquid and gas are all in equilibrium with each other, so any change of a state variable will mean that at least one of the phases disappears.

In order of increasing enthalpy, the states of matter are solid, liquid, gas, and plasma. Solids and liquids are collectively referred to as condensed matter. These states are characterised by strong intermolecular forces, which maintain local order by keeping distances between individual molecules or atoms within close bounds. However, in a liquid, bond angles can fluctuate on a short time scale, allowing the liquid to flow and change its shape. Condensed phases are resistant to compression; their compressibility, i.e. the volume change per unit pressure change, is low compared to gases. In gases, on the other hand, intermolecular forces don't play an important role, and the distribution of gas molecules in a given volume is largely random. Finally, in a plasma, the enthalpy of the system is high enough to ionise individual atoms; the material consists of atom cores and free electrons.

Both solids and liquids are characterised by short-range order: the way the nearest neighbours are arranged around each atom (of the same type) is fairly uniform. The interatomic distances are governed either by Coulomb potentials (ionic compounds) or by pair potentials (covalent materials). A substance is liquid if the strength of the interatomic interactions is comparable to the thermal energy, kBT. In this case, bonds can easily break and form again, resulting in a very flexible structure.

In a crystal the individual potentials are finely balanced, resulting in a periodic array of repeated local environments. Amorphous materials or glasses have a more liquid-like structure, except that bonds don't break and form dynamically. Short-range order is present in both types of solids, but only crystals have long-range order. The more disordered amorphous structure has a higher energy and is thus only metastable. To relax to the stable crystalline form, atoms would need to move across potential barriers and bonds may have to be broken. If the activation energy for such movements is large compared to the thermal energy, a glassy structure can be persistent.

Cited from http://users.aber.ac.uk/ruw/teach/334/condmat.php

In answer to the question in the title: yes - rock is definitely condensed matter.

Among the three (common) states of matter; solid, liquid and gas, the former two are condensed. Roughly speaking, in a condensed state, matter is essentially incompressible because decreasing the volume occupied by the matter would sample the strongly repulsive inner wall of the inter-atomic and inter-molecular interaction potentials at play. Enormous pressures are required to accomplish a very small decrease in volume for matter in a condensed state. In contrast, in the gaseous state, matter is easily compressible because molecules in a gas are essentially non-interacting and have zero volume. (These are basic assumptions of the kinetic theory of gasses, they define an "ideal gas".) There are two leading contribution to the non-ideality of real gasses: First, intermolecular interactions at long range lead to some attraction between gas molecules, leading to a slightly smaller predicted volume than the Ideal Gas Law would predict. When ambient thermal energy is too low (the temperature is too low) to overcome these weak attractive forces, the gas liquefies. Second: molecules have a very small but finite volume, placing a lower limit on the volume to which a gas can be compressed. (Further compression would sample the strongly repulsive inner wall of the inter-atomic and inter-molecular interaction potentials.) It is largely this second contribution that identifies a "condensed" state: the material is occupying the smallest possible volume. (Smallest reasonably possible, we aren't taking about neutron stars here.)

Carrying out MD simulations on "rock minerals" is plausible, but there are challenges. One of the most important will be that "rock" is not homogeneous over a wide range of length scales so a realistic simulation of say, granite or sandstone, for example, will almost certainly need to be multi-scale in nature. On the other hand, if you are interested in pure crystalline minerals, a good deal can be learned by carrying out calculations of the cohesive energy curve based on the structure of a single unit cell. For example, finding the cohesive energy curves for two different phases can reveal the pressure required to transform one phase to another. In principle, combining the results of such calculations with calculations of the phonon density of states can be the basis for predicting the P-T phase diagram for the material. Crystal structures are available for a huge range of minerals.

Dear Karl

I totally agree with you. About simulating rock minerals using MD simulation, I think there are several drawbacks currently:

1. As you said, the heterogeneity is the inherent property of rocks, so how to how to characterise the heterogeneity at micro-scale (atomic and/or molecular-scale ) and deal with the heterogeneity problem are of great importance.

2. Due to the limitation of computational power, the maximum size of simulated rocks using MD simulation is less than few millimetres, therefore, using multi-scale methods (aka, hybrid methods) is essential.

3. Because most simulation using MD simulation are related with clay (i.e., MMT), to the best of my knowledge, however, problems deal with other common minerals and rocks are relatively scarce (say, feldspar, granite), therefore, finding the appropriate force field for this minerals is another drawback.

4. How to validate the MD simulation of rock minerals.

By the way, I read some papers which mentioned simulating the soft condensed matter or soft matter using MD method, so here is another question, is rock soft condensed matter or soft matter?