Monitor Stands - Made of Stone

I have a history of using Stone inclusive of Granite for a variety of supporting roles in my own HiFi System.

I have used and still use Granite as outlined in the following:  Plinths @ approx' 90Kg each under Cabinet Speakers, a Plinth for a Garrard 401 @ approx' 90Kg, a Plinth Under Valve Mono's @ approx' 300Kg and Bespoke Built Rack Shelves @ approx' 25Kg. 

I have evolved with how I am utilising the Granite, it has not been used as a sole material for many years. It is used a Tier in a support Structure, and the position it is placed usually means it is a Upper Tier material which needs careful consideration for a footer being selected to be used.

I have never stopped working with materials that can be used in a structure in conjunction with the Granite.

Most recent, the material of Interest and being adopted is Phenolic Impregnated Densified Wood. This material comes in at 1400Kg per Cubic Metre, and measures for Damping and Dissipation in a much more desirable manner than Stone or Metals.

This material has made a impression on myself like few other materials have when used as a part within a Support Structure. The improvements on offer are seemingly tangible. 

I encourage the OP to look into this material to produce their design for a Speaker Support, it is finding a place in the construction of Hi End Speaker Cabinets and is being picked up on by other areas of the Audio Industry.    

Densified Wood is a name given that covers the methodologies used to produce the product.

Brand Names commonly selected are Panzerholz and Permali.

Panzerholz as a product is mostly used within Audio as the B25 material with the Wood Grain orientated as a Cross Grain on the Laminations.

Permali is usually EV6 again it is to have the Cross Grain Orientation on the laminations.

Each can be found as supplied boards with a thicknesses that ranges from 5mm - 100mm.

The Link will show a description offered by a individual who's career, will have introduced them to many options for a material to be selected. Panzerholz is quite important to the production of this Companies Designs.

  https://www.monoandstereo.com/2014/11/interview-with-rainer-weber-of-kaiser.html

Marble is a material to be avoided if function for a purpose is wanted over aesthetics only. 

I have never used Marble in the mass I have used Granite, but when including it in a structure, something of a detractor has been perceived as occurring with the sonic produced. The veil which is commonly referred to and enjoyed when perceived as having been removed, has as a result of my using Marble returned as being drawn and obscuring the view, this is quite noticeable when Marble is added to a Structure.

What will happen with a 250lb Mass of Stone Stand and Speaker used in conjunction with a purpose produced Suspension Plinth is an unknown to me.

My experience is that I have evolved to using a structure that has an upper tier with Granite utilised as a Plinth, which is to receive suspension footers to seat a Floor Standing Speaker on. 

The Suspension Methodology is an extremely good Corner Stone for a starting place, selecting the additions to the Speaker Supporting Structure such a upper plinth tier, stand material and design for the stand, is something that can maybe be subjected to further investigations.