This is a long one, but there's really no way around that except to bite the bullet and post the whole thing...

My spiritual path has come full circle, from the sense that burning inscence, especially sage, is the one thing that really works against evil spirits and negative energies (but would probably set off my allergies and make me sick to I don't dare) to working with crystal magic, to now describing myself as "Atheist, but when things get too weird, I burn sage and pray to the Gods." (and found out sage isn't too bad for my allergies)

How I came to this point - there are many reasons, but I'll start with the ones that might be helpful lessons for others.

I got into crystal magic as a "quick, do this, it'll help" measure from a Crystal Witch in what I can only describe as a Neopagan "Tech Support" network. I had no plan or had done any research. That came after the fact, as I prided myself on making "tribal" jewelry out of genuine natural materials - hemp stringing together beads of semiprecious stone, shell, and wood, seeing first-hand the effects of each mineral. (Wearing beads of one material on your skin circling a limb (especially an ankle) is the most overkill of everything I ever tried and if there's a positive (or negative) effect, you'll feel it quickly.)

This meshed with the New Age sentiment that artificial materials like plastic and metal are bad, even toxic (moreso than the government and corporations are letting on), and that crystals will do all sorts of beneficial things (well any mineral, but the pretty ones are more special) - grounding you, energizing you, healing your body, expanding your consciousness, healing your chakras, healing your spirit. The basic, simplest spiritual effects of each one seemed to prove true in (sort-of) single blind testing (writing down how wearing the stones made me feel before "looking up the answer" in the New Age books.)

The problem is that I also experienced something nobody (save the Crystal Witch) in the Pagan and New Age communities wants to talk about - crystals have limits. Crystals can cause problems. And artificial materials can be helpful in spiritual matters. (Yes, even those evil plastics!)

My thinking now is, using my analogy of spiritual energy being like electricity, one doesn't build a computer by making it out of nothing but superconductors. Conductors are there in the wiring, but the heart and soul is transistors and gates made of semiconductors. Insulating materials in-between to keep the current from bleeding to where it's not wanted.

Similarly, one does not build a spiritual life by simply surrounding yourself with nothing but crystals.

Here are the spiritual properties of materials (I personally observed) in order from most to least "conductive."

Quartz - I was originally told that quartz is the universal computer of crystals, able to be programmed with one's intent and do anything. That's the problem. It tends to soak up whatever energies are around it, taking in intent from those energies and playing it back over and over and over. Which makes it a double-edged sword against the very negative energies it purifies. I now think of quartz as a sponge - whatever it soaks up, it'll ooze back out slowly. (Yes, it can be "wrung out" so to speak, but I've yet to find a method that will completely purify a stone.)

Shell - Shells tend to be actively purifying if you wear them, but not so absorbing or general purpose as quartz. Like other minerals, they will eventually become saturated, though this can be mitigated by regular purification in salt water (a simulation of the sea they came from.) Necklaces and bracelets made of shell bits held up rather well spiritually, being purified along with me whenever I showered.

Semi-Precious Stones - Similar to quartz in that they too tend to soak up energies good and bad. Their properties vary widely, resonating with one's personal energy in many different ways, depending on the stone in question. I see them like Harry Potter shopping for his first wand - a mineral you need right now will resonate with you right away, gently, subtly, not in any way that's too strong or has side-effects. But now I temper that with the knowledge that yes, these too are sponges. Some minerals may ground or protect you... up to the point they become saturated with negative energy.

Metal - All metals, as I learned in my Properties of Materials class at university, have a crystal grain structure, which makes them similar in structure to ordinary stones like granite. Spiritually, metals also have a wide variety of properties, none of which were beneficial to my spiritual work. Wearing a pendant of silver, for example, seemed to prevent me from feeling any spiritual energy and raising power. On the other hand, maybe that could be a valuable protective effect in a different situation. As with other minerals, they will sponge up energy, but are trickier to cleanse as the usual "cleansers" like salt water and earth tend to ruin the finish.

Ordinary Stones - Common dull rocks like granite, sandstone, basalt, and so on. These are mostly only grounding, rarely (if ever) energizing like quartz or semi-precious stone. It's possible to use them as energy sinks simply by holding them in the palm of your hand... though anything from standing on them barefoot to rubbing them on your skin works too. They don't tend to actively pull in energy like quartz and semi-precious stones, only (mostly) absorbing what spiritual energy reaches them by conduction - physical touch. And yes, they too can become saturated with energy.

Wood - Wood tends to not readily hold any charge of spiritual energy... but it can, big time. You have to (usually) actively set out to charge it. I found wood without any charge or programming made an effective "moderator" material in bead patterns, keeping shells and semi-precious stones from becoming overwhelming. I'm not sure what other spiritual properties wood has, though in Celtic Astrology, the seasons are tied to different trees each with very different personalities and temperments (which are used a little in the Harry Potter books, the Elder Wand in particular.)

Cement - Think of it as artificial stone, but spiritually it always feels "off" to me, and is actually somewhat insulating. As I learned in the Properties of Materials class (and from some ecology writings which made portland cement sound like something from a toxic waste dump) it's more "tainted" with petroleum than even I knew. This makes it technically part plastic, and plastic (as I'll get to in a moment) is spiritual insulation. So is cement, but not quite to the same degree. Its most common effect is to separate urban areas from the Earth (This may be why many develloped areas seem full of negative energy.) On the other hand, a cement room would be protected from outside energies to a degree.

Plastic - Plastics resist spiritual energies. This is the insulator of spiritual materials. Anything made of plastic, whether just a toy, or a computer or phone with a plastic case, tends not to pick up spiritual charge, and "washes" it off readily if bathed in sage smoke. Plastic bags seem to work effectively like thin layers of radiation shielding, blocking spiritual energies from going in and out (a little - there don't seem to be any strong insulators for spiritual energy). This is such a valuable capability, I actually feel sorry for the previous generations that had to work magic with nothing really that could block out negative energies. All the methods of purification and exorcism that came before are in a sense stopgaps to work around having nothing that could really shield, though burning inscence and working ritual are active defenses and far more potent.

After experiencing all this first-hand, I now feel somewhat safe around modern, plastic objects, video game systems and so on. I know that, whatever is going on, they're the least likely to become "contaminated" with negative energies, cursed, and whatnot. My playstation will probably never "betray" me like a piece of quartz might. Yes, crystals are still quite helpful spiritually, but they are high maintenence, and I've come to regard the large pieces of quartz in my local magic shop with suspicion that would be alien to a New Ager... what sort of energy might they have picked up?