There are a wide variety of diamond necklaces, each with their own unique style and design. Here are some of the more popular diamond necklace types:

1. Diamond solitaire necklace: A single diamond, elegant setting, and necklace chain. A popular choice for formal occassions.
2. Diamond pendant necklace: A diamond pendant necklace usually features diamonds set in a decorative or ornate pendant made of precious metals. This can include cross necklaces or really any diamond adorned shape as the term pendant is used widely in the industry.
3. Diamond tennis necklace: Similar to the tennis bracelet, a diamond tennis necklace feautures a string of continuous diamonds that stretch around the neck. Diamond tennis necklaces are usually reserved for more elegant wardrobes and formal functions.

The short answer is yes, you can wear a diamond necklace everyday with just about any outfit. However, certain diamond necklace styles are more appropriate for everyday wear than others. For example, a diamond pendant necklace or diamond solitaire necklace are usually more suited for everyday wear than a diamond tennis necklace - both in terms of fashion pairings, design, durability, and price (diamond tennis necklaces are quite expensive and generally more formal, so most wearers probably wouldn't go to the grocery store in a diamond tennis necklace).

Diamond necklaces have always been and likely will always considered to be trendy or in fashion. Trends may come and go, but diamond necklaces are a timeless staple in the world of jewelry due to their versatility and brilliance.